will make this easy for you ;D
two red food dyes are used to colour the flesh of farmed salmon, canthaxanthin and astaxanthin – these are naturally occurring carotenoids. Salmon get these from their food of shrimps, krill etc this makes them nice and pink.
but when salmon are farmed and not fed naturally their flesh is and pale and the food manufactures think it is unappealing to consumers so – canthaxanthin and astaxanthin in a biochemical form as beta carotene are both are added to the feed of farmed salmon – this combined with chemical smoking additives makes it even more risky and many people as well as most dogs react to man made beta carotene
so whether smoked salmon or not – food dye is added to make the colour more appealing to humans – it is not good for doggies – they can get allergic reactions to it