White parts on the tails of otherwise self coloured mice often belie the fact that there is a marked gene in there somewhere.
Also to add onto this, Ive hear white tail marking can be associated with what are called k-factors, these determine how much white is on a mouse especially for spotted varieties. I think you can have k factors(or white tail tips/markings phenotypically) on a mouse that doesnt carry spotting though.MouseBreeder said:White parts on the tails of otherwise self coloured mice often belie the fact that there is a marked gene in there somewhere.