My cat Lulu

My cat Lulu is 2 years old, and within the last couple of days a bold patch has appeared on her stomach. She doesn't seem overly bothered by it, and i have posted photos of her belly. Also her nipple keep changing from white to pink then back again, im not sure whether it is because we have 2-3 week old kittens in the house (not hers) or because of another reason. I am worried and wondering if i should take her to the vets or not. I would appreciate anyone who make know why these things are happening or any opinions.  

Did you forget the pics?

I did upload them on my profile, but im not sure how to post them here, sorry i am new to this site

Here they are

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Aww, can't help but love a pink belly!
So her nipple changing colour is unusual. Is there any way the kittens could be suckling on her occasionally? Sounds like the nipple is getting irritated somehow.

We also have 2 four month old kittens, and one of them suckles on the other. So i am wondering if it's possible that they are also suckling on Lulu, your point made me think this, so thank you. That explains the nipple situation. However, my cat Lulu still has a bold belly, it's clean so it's not cat acne. It at first looked like she had been shaved, but she hasn't, her belly doesn't seem to be sore or irritable currently. Only one of her nipples, it seems as though she has caught her belly and nipple on something causing loss of hair. But i am not sure, the photos are there to see, hoping with help I/we can get to the bottom of this. Thank you for you comments, any more thoughts or opinions are appreciated