Rainbow patina?

I've recently got several 1974 Mozambique 20 centavos
 https://en.numista.com/catalogue/pieces5517.html
and a couple of them have what looks like rainbow patina which sometimes covers up to 90% of the coin surface. In general, coins look quite pristine - from AU to UNC but this unusually colored  patina bothers me.
Is it worth to keep it and does it have a value which differs (up or down) from a value of a regular UNC coin?

Thanks
Eugene
 

If you post pics we could tell if it is genuine or not.

OK, will take a picture tomorrow

Here are the pictures - straight from the camera, no image editing, just cropping. Left - regular one, right - "rainbow". Any comments?

nice colorful coin nice toning should be worth a lil more

Sorry about taking so long to respond.

I don't like the look of the toning-  it looks to me like it has been heated to create the rainbow effect.

Guys,
Thanks for your replies, my learning curve is still ahead of me..
I'll keep the coin  anyhow but will keep in mind that it may be an effect of the artificial treatment. BTW - do you have any picture of a "genuine" rainbow patina?
Eugene

Check this thread out on the coinshow radio forum.

http://www.coinshowforum.com/index.php?/topic/101-toned-coin-thread/

Thanks, I have to agree with you that my "rainbow" looks very differently from those examples.