GT250R 2007 Chain

Hi:  I have a 2007 GT250R brought 2nd / 3rd Hand.  Really good condition.  There is one thing that is perplexing me, the chain.  The chain has tight and slack spots in it.  I go to check the chain tension the chain appears to be slack 50mm play I rotate the rear tyre and a section of the chain appears to be tight little 15mm or no movement. Any well thought out and sensible suggestions as to cause and remedy would be gratefully appreciated.

PS. While I’m here does anyone know the paint code for the engine the (browny-goldy-metallic) colour.

Cheers

Frank5168