Assuming that the color has nothing to do with an actual reaction with the floor, a yellow color for HCl is common as concentrated HCl liquid itself often has a clear to light yellow color. Pour some out in a beaker and see if the yellow color is coming from the liquid itself. The yellow color in HCl is due to trace amounts of impurities such as chlorine gas, iron, or organic molecule impurities. Even if you start off with a "pure" clear HCl solution, over time it will turn more and more yellow as it is exposed to the air and as it eats into the ccontainer you are storing it in. I see this all the time as the HCl we use for the swimming pool is now quite yellow after having sat around for a while.