Pretty much anything will catch brookies. I have caught them on Royal Wulffs when all that was left was a pair of wings and some unraveling thread. I would use those, small hoppers, anything bushy like an EHC, and if you want to fish subsurface, a small olive or black bugger is all you need. In lakes, we usually only bother with buggers in #10 and foam hoppers in 12 or 14.

I don't think there are any brookie streams BELOW 5000 feet in Colorado, are there? Anything much below my 5700' is warmwater.