computing I-mag from V-mag, how to?

["Yegor"]

Hi,

We are interested in star I magnitudes.  Hipparcus catalog has
V-magnitudes.  Is it possible to compute I-magnitudes from
V-magnitudes?  Is that what the V-I mag field is for?  If so, how to
use it?

Also, what is the ratio of red stars to blue stars (or a good web
resources to find out)?

Thanks a bunch!