Is it 4?
Bags 1 2 and 3.
Check bag 1. blue.
Check bag 2. If blue, check bag 2 again. if red check bag 3. (if checked twice and one of each colour, bag 2 is both, bag 1 is blue, bag 3 is red)
Check bag 3. If blue, check bag 3 again. if red check bag 3 again. (if checked twice and one of each colour, bag 3 is both, bag 1 is blue and bag 2 is red)
