You can go to color swatches in tools and look at the numbers labeled on the yellow shades. I assume they are from 41-49.
Then use the command set color 41 + random 9.
That's right! If you want less black / white (smaller range of yellows), then you can also do
SET COLOR 43 + RANDOM 5
You can do
let greenum (100 +(random 100))
set color (list greenum greenum 0 (50 + (random 50)))