Exporting to GIF

[kayvee]

I'm trying to decide whether I should buy OmniGraffle for making a 
large number of charts for a web-based course. When I export to GIF, 
all the colors are pixelated and lighter, and the type is very faint. I 
am using web-safe colors (but that shouldn't make a difference anyway.) 
When I exported to JPG, the colors were truer but the background was 
black.

I want this to be easier than Illustrator!

Advice?

thanks,
Karyn