Sudoku Line Colors

by ChinStrap and gdc
sudokucolors.netlify.app

Standard colors for sudoku lines are too strong. They obscure pencilmarks and are fatiguing to look at for too long. We are proposing a set of colors that setters can use to have more readable lines.

The table below contains our proposed new colors and a comparison to the current standard colors. Readability of pencilmarks in our new colors are improved without sacrificing distinguishability.

Frequently Asked Questions

The table above has a list of all our suggested colors, what lines we recommend using them for, and the hex code of the color itself to be used in whatever tool you wish to use.
Clicking on the table also shows a full 9x9 preview of the color and gives access to a colorpicker to customize those recommended colors.

Using the OKLCH colorspace, we picked a variety of colors that shared similar perceived lightness and chroma (saturation of color), and mainly only varied the hue (position in the color wheel). The main goal was to keep a perceived lightness that was consistent between colors, while making pencilmarks more readable, especially with colors close to blue which tend to clash with the blue numbering.
For the comparison colors, most of them were collected from SudokuMaker and f-puzzes (rangsk plugin) since they are very widely used on LMD. The remaining three comparison colors (red, blue, purple) were made up to complete the overall pattern of these colors.

This is not intended as a color deficiency friendly palette, but instead one optimized for readability. There are many kinds of deficiencies and no palette can satisfy them all. Making puzzles more accessible should involve methods other than colors (for example: different line styling for different colors, or lettering individual lines) and is beyond the scope of this.
If you want to optimize colors for color vision deficiencies, a good place to start is Coloring for Colorblindness. A puzzle that uses lettering can be found here. An example for lines with patterns can be found here and here.

If you click on the "preview" column in the table above, the correponding color will be displayed with an example puzzle. Below the example puzzle, there are sliders to modify the color. Clicking on the example puzzle also changes the puzzle.
The sliders use oklch coordinates which might take a little bit of time to get ued to. But once you play around with it and get some intuition, it will hopefully become clear why this was chosen over the more conventional hsl or rgb coordinates.

If you have a puzzle that you suspect coloring will come into play, it is best practice to create a slightly white outline when making lines, by drawing a white line that is 20% thicker behind every colored line. Alternatively, you can also draw a thinner white line above your line to get a "hollow" effect. If this doesn't work for your particular puzzle, that is okay, but it is often times very helpful.
An example where both these techniques (outlines and hollow lines) are used can be found here.

Hex can represent millions of different colors. But there are colors perceivable by the human eye that don't have a hex representation and can't be displayed by most monitors. Additionally, setting tools like f-puzzles and Sudokumaker only accept hex colors as inputs. For those reasons, this color picker limits the choices to colors with a hex representation.
This leads to "gaps" in the sliders since a bright blue has a lower maximum saturation than a bright yellow. If you choose a color outside of the hex-range, it will be replaced by the closest possible hex color via a technique called "gamut correction".