All US made engines were 100% Ford blue. However De Tomaso's stock of US made engines was used up by 1976 or sooner. Your 1982 GT5 Panteras engine should have been sourced from Ford of Australia.
Its easy to distinguish the two engines. All the US engines had big port "4V" heads, the Australian engines had small port heads. The US engines have a "CF" symbol cast into the rear of the block in the same area as where the oil pressure sensor screws into the block. Australian engines have a "GF" symbol cast into the same area. US engines have a "4" cast into the upper corners of the cylinder heads, Australian cylinder heads have no number cast into the corner.
If the engine is Australian it would have came in one of 3 color schemes.
(1) 100% Ford blue (all engines through 1978 with one exception).
(2) Mostly Ford blue except for orange valve covers (this is the exception, 1972 - 1976 engines with 2bbl carbs).
(3) Black block & heads, silver valve covers and air filter assembly (all engines post 1978, i.e. 1979 - 1985).
Your 1982 Pantera should have had a black/silver engine. The tell-tale sign is the distributor, is it a Motorcraft distributor with breaker points, or a Bosch breakerless distributor? The distributors had different shaft diameters and they don't interchange. The black/silver engines had Bosch distributors.
My Australian friends are welcome to correct me where I'm wrong.
Martijn, how about a picture of your Pantera?