To change your brush to the appropriate color simply press one of the paints at the bottom. If you wish to start over press the space bar or click the green flag. To switch to a long-furred cat press 2. Otherwise, press 1 to switch to a short furred cat.
Not all Warrior Cat generators have the features you might want in your warrior. So why not draw it instead? Granted, I realize that I limit certain features as well, but we can't all be winners.