Smaller dogs do not bleed as much as larger breed dogs; however the amount varies from dog to dog. In any event, there will be some blood that discharges from her vagina and her vulva will become swollen.
You may not notice any blood as it may just be trace amounts. It can vary from red to a light pink. Toward the end of the cycle it can appear to be more of a light tan.
She may have a tendency to self clean by licking, however if you notice that any discharge has dried and become stuck to the coat, you can remove it with baby wipes.
Even if your Yorkie appears to have just a slight discharge, over the course of days and up to 3 weeks, this will accumulate on bedding, flooring, furniture and more.
For this reason, you will want to place doggie diapers on your dog while she is in the active stage of heat to absorb and contain the blood and other bodily fluids. Many owners opt to place a pretty canine panties over that just so that the dog looks cute.