Instead of adding yet another tag for only cycle lanes with all its problems in case of multiple lanes with different colors, would it not be a better approach to stick to a more general system by using the :lanes tagging?
Example (from left to right: two lanes without restriction, a shared, green lane for bus and bicycle, another lane without restriction, a red cycle lane)
lanes=4
oneway=yes
access:lanes=||no||no
bicycle:lanes=||yes||designated
bus:lanes=||designated||no
cycleway:lanes=no|no|share_busway|no|lane
surface:colour:lanes=||green||red
Edit: Add a description for the lanes and count the bus lane as lanes=*