Chroma Question

Helllloooo! I was just wondering if anyone could tell me how often chroma's go on sale? I took a huge break from league not too long ago. So I missed a lot to do with the chroma skins. I have seen a lot of people talking about how they go on sale for IP every now and again. With a big purchase I am about to make soon. I would like to know if I should use my left over RP to buy a chroma, or wait for sales and buy them with IP.

Thanks for the help!