I finally downloaded Dots, only to find that I’m far too colorblind to actually be good at this.
Sara Lang, unaware the game had a colourblind mode. Via Twitter.

Accessibility features are not yet a standard expectation, players often do not know to go looking for them. Without signposting, some of the work on those features can go to waste.

Several techniques are possible. Showing the menu itself before the game starts. Building them in to the intial tutorial, as is sometimes done for features such as stick inversion. Highlighting features on initial and interstitial loading screens. Even prompting players about them if it looks like they might be having difficulty.

Best practice example: Battlefield Hardline
Best practice example: Block
Best practice example: Nier Automata