[3.0dev] Low priority - provide picker for transition color

[LindsayHill]

We now provide user over-ride for transition arrow colors, rather than defaulting to success == green, failure == red.

This is good.

But it is not immediately obvious what options users have, or what the syntax is.

Should we provide some sort of drop-down list of colors, or similar?

[LindsayHill]

Alternative - provide a tool-tip that gives users examples of what they can enter in that box

[enykeev]

Adri actually designed one for us (see https://docs.google.com/document/d/1KY5LPqK6M4Fhlb8Sw4rvDkcLsyZeonP3XaYk4js83Sc/edit?disco=AAAACWcd5o8). Someone just needs to implement it.