Howdo Freesky
I have a couple of lovely split sea-polished pebbles of brick-red flint. Flint occurs in all sorts of colours. My native flint is grey with white speckles but I regularly find orange, white and black flint. I'm told the orange flint comes from Fife via longshore drift and glacial transportation, the others have probably eroded our of the glacial till. I was over in Cumbria a few weeks ago and was shown some beautiful jet black chert tools collected from the Mallerstang valley.
As for formation, I guess Spaceship Mark could give you more detail, I always thought that the red/orange colouration was down to the iron
content when the material was deposited however flint definitely changes colour when exposed and weathered.
I'm not sure if this applies in the uk, further afield red jasper was used for prehistoric tool making, it has a concoidal fracture and therefore can be knapped in the same way as flint.
cheers
fitz