Where In Colorado are you headed? You can prospect for Gold in Denver (I do). You could contact any of the Gold Prospecting clubs in Colorado to see what they are doing during the times you will be in the state - maybe you can join them.
As is always the case - Gold is where you find it. Read up about the Colorado Mineral Belt, and compare that to where you are planning to be - then start searching the internet for any of the places that look interesting that are in areas that have a history of finding gold. You may find places that are open for panning where Placer gold is known to exist. There is gold outside of the mineral belt area too - so you may have too many places to research before the summer.