Chevrolet engine paint colors

I've got a quick question for any Chevrolet mechanics or others for that matter.
When did GM change the engine paint colors on their engines?
I remember Chevrolet orange from when I was a kid.
Then there is Chevrolet blue on my 1979 ElCamino.
I'm putting a cam in a 1984 Chevy pickup and started to paint the intake orange but noticed the valve covers were painted black after I got the grease and oil off of them.
Technically, what color should they be?

Chevrolet used the orange up until the late 70s, somewhere around 77. Thats when they changed over to the blue color because of the big issue of company engine swaps. You would find Chevy engines in Pontiacs and other cars. GM released to the press that all engine were built by GM and reserved the rights to put them into what ever car they wanted to. Then by the mid 80s some where around 85 to 86 Gm started painting the engines black because of mechanic complaints. Evedently they were having trouble finding oil leaks. By painting the engine black and adding floresant die to the oil and using a black lite the leaks became easier to track. Thus the black engine color which is still used to day by almost all the car companies. I hope this is helpful to you.