Logistic regression can handle categorical predictor variables, too. Similarly, the values to predict "red", "blue" were stored as strings. You can use numeric 0 and 1 if you wish. Logistic regression ...

Lin HY, Desmond R, Louis Bridges S Jr, Soong SJ (2008) Variable selection in logistic regression for detecting SNP–SNP interactions: the rheumatoid arthritis example. Eur J Hum Genet 16(6):735–741 ...