Ultra-violet. Only bees and snakes and a few other things can see it (snails, hopefully?). But you know... crayon-box color wise... purple. And red-orange. But NOT orange-red or red or orange! My favorite type of purple is "Fairytale purple" its sort of... i dunno. lavender, but a more magical lavender. i also like "20s green" which is sort of light green, like the colour of a lot of dresses in the 20s i think....