Is my cat's incision healing properly?

Is my cats spat incision healing properly? The picture isn't. Brilliant but there is quite a large, hard lump under it and her incision has a small amount of slightly yellow crust around the stitch. I'm worried something is wrong. She went straight back to her normal self 1 day after the op! I kept her in the bathroom so she could rest (as the vet told me to confine her so she could rest for a few days). But she was up on her feet after 1 day of rest. She's eating and drinking fine, the lump and incision are not hot or hurting her. She doesn't lick or bite at it. She's happy and playful. Not sure if I should be worried by these things. Someone help?

Im not an expert Vickie, but in my experience the yellowing is normal, but the hard lump is not. I would contact your vet asap, and ask them, and tell them you have a picture, you might be able to send the vet the picture first before claiming another office visit.