Looks like you have a varigated variety.

MrsG is correct, you have a variegated lemon. What is the cultivar name of your lemon? If it's 'Pink Lemonade', this is a variegated lemon cultivar with pink tinged flesh. Pretty tree, pretty fruit (which also starts out variegated when it's green), but not the juiciest lemon out there. Mainly grown for it's very lovely foliage. If this is just a branch that popped up and is sporting variegation, you're seeing what citrus do here and there - sport interesting genetic differences. You can cut off a piece of budwood from this sport, and graft to citrus rootstock, and grow an entirely variegated cultivar. And, I might suggest if you have citrus questions, to post over on the Citrus Forum.

Patty S.