The first simple answer is that blue interior was not a standard color with black exterior, therefore you probably have grey.
The grey interior was slightly darker on the 1988-1989 cars than on the later ones. I believe if you had blue it would be obvious as the blue is dark.
The final answer.... look in the trunk, next to the spare tire. at about the 3 o'clock position, raise the insulation and you will find a label with lots of numbers. Copy all those codes on a piece of paper and then go to
www.reatta.net and look under codes and you can decode the codes.
near the bottom of all the numbers, you will have one code that is 41U that is the code for black exterior. I suspect you will also have 15F, 159, 15I, 15=grey. If you have blue interior the number will be 20.