My female blows her coat profusely the month before her heat, she loses her hair all over quite extensively. As a puppy when she does it, her coat color did change. I don't remember it being patchy but I know she came out lighter. She was light, then real dark, then lighter, darker, etc... The picture you showed looks ok on computer. Do you see a lot of hair being shed around the house?
How does the skin underneath look?
If she's going into heat, not sure if that's a good time to get spayed. Maybe let her go through one round (if you can handle it) and take her in after that.