27 August 2025

Helium: A Wedding Between Selenized and OKSolar Color Schemes

by Raymond K. Zhao

Solarized Dark is a famous dark color scheme for code editors and terminals. However, personally I was never a big fan of it, mainly due to the following issues:

Its contrast is too low.
Accent colors such as green and yellow are not very distinguishable.

From Wikipedia, there were two efforts, namely Selenized and OKSolar, trying to solve the issues above. However, by design, OKSolar did not try to solve the second issue and the contrast between emphasis and normal colors is kept low. On the other hand, Selenized has more distinguishable colors but it is too bright.

So here comes to the question:

Could we combine the approach of OKSolar, which has more uniform color brightness, and the color palette of Selenized, into a single color scheme?

I did some experiments during the past weekend and created a color scheme called Helium ^[1], which is also used by this website at the time of writing. You can see from the result that green and yellow are distinguishable, different foreground / background colors have a bit of contrast, and the colors are not too bright.

Color Spaces

Here are some backgrounds on the color spaces used by Selenized and OKSolar. Instead of RGB, colors in both color schemes are defined in the tuple $(L,a,b)$ , where $L$ is the lightness, $a$ is the green-red channel, and $b$ is the blue-yellow channel. The Cartesian coordinate $(a,b)$ can be converted to the polar coordinate $(c,h)$ , where $c=\sqrt{a^2+b^2}$ is the chroma, and $h=\mathrm{atan2}(b,a)$ is the hue.

Selenized uses the older CIELab color space, while OKSolar uses the newer OKLab color space with better perceptual uniformity. For each color, the RGB values are derived from $(L,a,b)$ or the equivalent $(L,c,h)$ in that color space.

Color Palette of Selenized

Now, let us examine the colors in Selenized. Fortunately, the author provided the script of generating the color palette. From the script, every color in the palette can be derived from the background color bg_0 and the foreground color fg_0.

Here I only focus on the Selenized Dark. The following snippets are the simplified version of the script for the specific bg_0 and fg_0 used in Selenized Dark.

### MONOTONES

monotones = {
    "bg_0": [bg_l, bg_a, bg_b],
    "fg_0": [fg_l, fg_a, fg_b],
}

# define additional monotones using contrast
# (0 - lightness like in bg, 1 - like in fg)
# For some reason bright background looks washed out without increased saturation
monotone_spec = {
    "bg_1":  [1/10,  1.2],
    "bg_2":  [1/4,   1.2],
    "dim_0": [5/8,   1],
    "fg_1":  [1+1/5, 1],
}

# use weighted average.
def expand_monotone(spec):
    relative_lightness, extra_saturation = spec
    l = bg_l + relative_lightness * (fg_l - bg_l)
    fg_weight = min(relative_lightness, 1)
    bg_weight = max(1 - relative_lightness, 0)
    a = (fg_weight*fg_a + bg_weight*bg_a) * extra_saturation
    b = (fg_weight*fg_b + bg_weight*bg_b) * extra_saturation
    return [l, a, b]

for name in monotone_spec:
    monotones[name] = expand_monotone(monotone_spec[name])

bg_l and fg_l are the $L$ of bg_0 and fg_0, respectively. Let $K=\mathtt{fg\_l}-\mathtt{bg\_l}$ be the contrast between fg_0 and bg_0. $L$ of other monotone colors are derived as $L=\mathtt{bg\_l}+w_MK$ for some constant $w_M$ .

The $(a,b)$ of these colors are also adjusted using weighted average between fg_0 and bg_0 with weight $w_M$ . In Selenized Dark, because $\mathtt{bg\_0}=(23,-12,-12)$ and $\mathtt{fg\_0}=(75,-5,-2)$ , fg_0 has lower chroma than bg_0. Thus, this weighted average will certainly lower the chroma. The script acknowledged the issue and multiplies the weighted average by 1.2.

### ACCENTS

# accent colors lightness shouldn't be exactly uniform, but on the other
# hand they shouldn't be too far away from each other.
accent_l_spread = (fg_l - bg_l)/3

accents = {
    "red":      [fg_l - 0.84*accent_l_spread,  63,  40],
    "orange":   [fg_l - 0.48*accent_l_spread,  37,  50],
    "yellow":   [fg_l - 0.00*accent_l_spread,   6,  68],
    "green":    [fg_l - 0.36*accent_l_spread, -38,  55],
    "cyan":     [fg_l - 0.12*accent_l_spread, -40,  -4],
    "blue":     [fg_l - 0.84*accent_l_spread,   0, -57],
    "violet":   [fg_l - 0.66*accent_l_spread,  30, -45],
    "magenta":  [fg_l - 0.50*accent_l_spread,  55, -15],
}

# bright accents have the same a* b* coords as regular accents and
# uniformly shifted lightness
br_accent_shift = (fg_l - bg_l)/10

br_accents = {
    'br_'+name: [l + br_accent_shift, a, b]
    for name, [l, a, b]
    in accents.items()
}

Here, $L$ of each accent color is derived as $L=\mathtt{fg\_l}-w_A\times\frac{K}{3}$ for some constant $w_A$ . Note that the accent colors have non-uniform lightness by design. $L$ in the bright variant of each accent color is increased by $\frac{K}{10}$ .

Creating Helium

In this section, all colors are represented as $(L,c,h)$ in the OKLab color space, using the OKLCH Color Picker & Converter.

First, let us compare the $L$ and $K$ between foreground (i.e., fg_0) and background (i.e., bg_0) in Solarized Dark / Selenized Dark / OKSolar Dark.

Solarized Dark	$L$	$c$	$h$
Foreground	0.6536	0.0195	203.55
Background	0.2649	0.0523	218.89
$K$	0.3887

Selenized Dark	$L$	$c$	$h$
Foreground	0.7831	0.0157	199.15
Background	0.3339	0.0512	219.52
$K$	0.4492

OKSolar Dark	$L$	$c$	$h$
Foreground	0.718	0.017	198
Background	0.274	0.05	219.6
$K$	0.444

You can see Selenized Dark > OKSolar Dark > Solarized Dark in terms of both $L$ and $K$ . Compared to the Solarized Dark, OKSolar Dark uses a similar $L$ in background and increases $L$ in foreground to improve the contrast. On the other hand, in Selenized Dark, although $K$ is similar to OKSolar Dark, $L$ in both background and foreground are increased.

I decided to use the foreground and background of OKSolar Dark for Helium, because it has higher contrast than Solarized Dark, while not being too bright as Selenized Dark.

To adopt the color palette of Selenized, I followed the snippets above, but using $(L,c,h)$ in the OKLab color space instead. There are some notable changes:

Similar to OKSolar, I used the same $(c,h)$ in {bg_0, bg_1, bg_2} and {fg_0, dim_0, fg_1}, respectively, i.e., only changing $L$ in each set. This would also solve the problem of reduced chroma in the original script.
Similar to OKSolar, I used the uniform lightness i.e., same $L$ for all accent colors. To minimize the average difference of $L$ with the original colors in Selenized Dark, I used a fixed $w_A=0.49$ for all accent colors in Helium, which is the median value of all $w_A$ used in the original colors.

Here is the color palette of Helium. Enjoy!

Helium	$L$	$c$	$h$	RGB
`bg_0`	0.2740	0.0500	219.60	#002d38
`fg_0`	0.7180	0.0170	198.00	#98a7a8
`bg_1`	0.3184	0.0500	219.60	#0d3844
`bg_2`	0.3850	0.0500	219.60	#214a56
`dim_0`	0.5515	0.0170	198.00	#677575
`fg_1`	0.8068	0.0170	198.00	#b4c3c4
`red`	0.6455	0.2008	26.30	#ef4c47
`orange`	0.6455	0.1472	49.30	#d36e2f
`yellow`	0.6455	0.1476	90.77	#b08800
`green`	0.6455	0.1738	133.21	#60a319
`cyan`	0.6455	0.1159	184.88	#00a497
`blue`	0.6455	0.1649	255.25	#3f8eef
`violet`	0.6455	0.1449	300.58	#9d77d8
`magenta`	0.6455	0.1736	346.16	#d55aa4
`br_red`	0.6899	0.2008	26.30	#ff5b54
`br_orange`	0.6899	0.1472	49.30	#e27c3e
`br_yellow`	0.6899	0.1476	90.77	#be9600
`br_green`	0.6899	0.1738	133.21	#6eb12e
`br_cyan`	0.6899	0.1159	184.88	#20b2a4
`br_blue`	0.6899	0.1649	255.25	#4d9cff
`br_violet`	0.6899	0.1449	300.58	#aa84e7
`br_magenta`	0.6899	0.1736	346.16	#e468b1

2025-10-09: Because both the Solarized Dark and Light palattes are used in the same Geany theme, I created the light variant of Helium by keeping the same accent colors.

Note: The Helium Light has even lower contrast than the original Solarized.

Helium Light	$L$	$c$	$h$	RGB
`bg_0`	0.9730	0.0310	90.00	#fef6df
`fg_0`	0.5816	0.0170	219.60	#707d82
`bg_1`	0.9339	0.0310	90.00	#f1e9d2
`bg_2`	0.8751	0.0310	90.00	#ded5bf
`dim_0`	0.7284	0.0170	219.60	#9caaaf
`fg_1`	0.5033	0.0170	219.60	#5a676b
`br_red`	0.6064	0.2008	26.30	#e13e3b
`br_orange`	0.6064	0.1472	49.30	#c66220
`br_yellow`	0.6064	0.1476	90.77	#a27d00
`br_green`	0.6064	0.1738	133.21	#559600
`br_cyan`	0.6064	0.1159	184.88	#00988b
`br_blue`	0.6064	0.1649	255.25	#3282e2
`br_violet`	0.6064	0.1449	300.58	#916bcb
`br_magenta`	0.6064	0.1736	346.16	#c74e97

1. The name Selenized was derived from the chemical element Selenium, which was named after the Greek goddess of the moon Selene. Thus, I decided to call my color scheme Helium, the chemical element named after the Greek god of the sun Helios. Helium is also known to glow under high voltage and was used in lasers.

tags: Misc