Mr. Laser Beam wrote:
Assuming this is the case: why, in ENT, is there no red?
Trick of the studio lights. The stripes photograph differently on the sets, depending on reflections.
For TNG, they deliberately colour-shifted all three designations. Red to a wine/cherry (since the movies were now using a similar tone for their uniform jackets), blue to a teal and gold to a mustard. Check out the "Enterprise" action figures: they used a red paint for the engineering stripes, not purple.
One reason for the avoidance of a straight blue dates back to TMP, to avoid it being the same blue as an original SPFX bluescreen of the late 70s. For TMP, sciences division was broken into two colours: orange
for science and mint green