Look at B-52s.. how many of them are down in the dirt flying around? Why did they put camo all over those? I've been trying to figure it out myself.
B-52's did indeed go to low level penetration tactics as Soviet radar and defenses improved. The B-52 was originally designed as a high altitude bombers, but by 1960 it was apparent that low level enhancement and tactics would be required (Lloyd, 6) The last model, the H, was the only version specifically designed from the start for low level work. Other models were upgraded with low level radar, improved altimeter, better cooling, structural improvements etc. Wing cracking later required stronger wing skins.
Gradually the fleet was painted, although some early models remained in natural metal and anti-flash undersides their entire lives. By the mid 1960's many were painted. There was a variety of paint schemes to better suit the low level mission. SAC three tone scheme, SEA scheme, SEA scheme with gloss black undersides, SIOP scheme, and later on all over gray.
Ref: Lloyd, Alwyn. B-52 in detail and scale.