TextMate: Conditional formatting?

Question

I want to be able to color lines differently based on the starting character.

eg.:

- This is line 1
- This is line 2
x This is line 3
- This is line 4
x This is line 5

So lines 1,2,4 (starting with '-') should be blue while lines 3,5 (starting with 'x') should be red.

Is this possible? How would you do it?

Thanks.