Colour and accessibility

Blockly uses colour as a strong hint about the role of each block, and to group blocks together. For the included blocks, this affordance is secondary to the text on the block, and so not a critical attribute. However, when choosing a block colour palette, colour blindness should be a consideration.

Blockly provides several themes in an effort to accommodate some types of colour vision deficiency. This page includes example 8, 12, 15, and 24 colour palettes that attempt to maximize distinction across the most common forms of colour blindness. Note that this wouldn't map to 8, 12, 15, or 24 block categories in Blockly, because some shades should be reserved for shadow blocks and fields.