Second week of june is typically prime season in colorado. Last year we experienced a some rain and cool weather in june which kept the flows dampened, always a possibility this year too. Its as good of a time to plan a trip as any other.
Mid june is usually good for CB creeks. Gore typically is running very high and is a burly V+ at high flows.
Snowpack is decent. Most of the southern part of the state had an average snow year. Northern part of the state and front range was in the 80ish % of average, which is lower than we would like, but still enough snow to have a decent season.
is a good online run listing and flows resource. Spend a lot of time planning your trip out using those resources. A CO guidebook and a gazatteer would be helpful too.
For IV to V- creeks... I'd look into bailey on the north fork of the south platte, clear creek of the arkansas, black rock on clear creek, castle creek into slaughterhouse on the roaring fork, maybe crested butte creeks.
I'd try to get an idea of where the runs are and what the drive times are between parts of the state. Get a hit list of runs you think you would like, and check flows just prior to your trip to try and finalize a good itinerary.
Whitewater of the southern rockies is a good guidebook. One thing I find useful is it has a 5 star quality rating for runs that can help boaters try and choose between runs and keep you on good stuff. The WWSR also has a very good breakdown of flows that correspond to min/low/med/high and the difficulty for each flow level. This is very helpful when trying to gauge if runs are flowing good or not.
Enjoy the trip!