I don't think it is a photo effect. The loco is moulded in green and self-coloured, the tender is moulded in black and painted. On the original photos (in sunlight) it's noticeable, less so in artificial light, but once you know...
The smoke deflectors put up a fight, but I beat 'em. Interestingly they were located with four pins in holes each side, only two of which had glue in them. A bit of cutting and filling required, but #1 son has nicked my Milliput...