Colourful herbs

Thyme's always good, comes in a few varieties as well (I've got two varieties planted in my garden - a bluish traily one and a yellow bushy one), then there's good old lavendar, I'm not sure if it's technically classified as a herb, but it smells great, is fab for colour (blue/silver) and grows pretty big and fills out beds too

hth

EDIT: I'm pretty sure Sage comes in a few varieties as well

 

Colourful sage varieties aplenty. Purple, yellow/green variegated, silver white. ALl good for the pot too.
Perilla frutescens comes in astonishing shades of purple and carmine.

Purple basil is easily available (also the seeds) and tastes great, somewhat different from most ofthe green ones. Gorgeous for chimichurri sauce.
Melissa and mints come also in variegated forms.