Hi Fancybaker 
I agree with Julia on needing to add lots of wilton colour (I love wilton for pale colours but rarely use them for strong), some brands seem to colour better than others so you might want to try a few different ones to see whats best for you. I use Americolor for stronger colours and have found I don't need to use anywhere near as much gel as I do with wilton - it's also much easier to add out the little squirty bottles too. I usually don't get staining except for black - you get a bit of a black tongue but it doesn't seem to be as bad as with Wilton.
The rainbow dust range colours well - but I have found colours like red tasted pretty bad even though the strength of the colour was fantastic (whole family now calls them the stinky colours), so I don't use them anymore, though I know lots of people really like them. (it could just be us )
Hope that helps and nice to meet you 
Looking forward to seeing your cookies and lovely bright colours.
Marie