I'm not sure what to suggest other than perhaps contacting the British Motor Industry Heritage Trust with those kinds of detailed production survey of detailed production survey questions. You might also contact Charles Runyon at Roadster Factory since he seems to have a handle on some arcane information.
My anecdotal evidence of what has been listed as standard colors for the TR250 (in other words based on TR250s that I've seen with my own eyes over the years) suggest that something on the order a third to half of them were in Jasmine with black interiors. Signal Red with black interior seems to make up something on the order of a quarter to a third. Of the remaining five colors Triumph used Racing Green is next, followed by White and Royal Blue. The two least common colors are Valencia Blue (I've seen two originally in that color and one that was a color change from Jasmine) and Wedgwood Blue which was a TR4/TR4A color supposedly used on some early ones but I don't recall ever seeing a TR250 in Wedgwood.
My color observations could be biased by region as other regions might have received different color mixes than across the southern tier of states. I'd welcome anyone's observations on what they've seen in their area especially if different.