Hi Stephen,
I could be wrong but I think we have discussed it before.
I can only offer my slant on things based on my experience.
My local TA's tikka and tandoori, which doesn't have a tandoor by the way, are very different.
As you say, tandoori tends to be red, whereby tikka is yellow to orange but they also taste different.
Their lamb tikka, and tandoori chicken both taste the same. They have a definate minty note to both of them, so I would suggest that they use the same marinade for these. However, their chicken tikka, tastes and looks completely different.
Their chicken tikka is a yellowy orange colour, and tastes very savoury, and I can difinately taste methi (fenugreek) in there.
My local TA is Pakistani owned, which may explain the differences I experience but I would suggest that, what they do is typical of the food around this part of Manchester.
Ray
