there is no problem in mixing the two types, which one you choose to use will depend on where your reservior is situated (is it close to a constant heat source) and whether or not you intend to use the bike all year round or just summer?
basicaly the red oil is recommended for ambient temps between 20 - 40C
blue is recommended for ambients between 0 -20C
which ever one you choose the flow rate will still need adjusting through out the year.
blue is the standard oil recommended for UK use, and i use it all year round.
hope that helps