The blue looks lighter on the HST power car, and I've thought the same thing about that one that they recently repainted in the same scheme. You're eyes are not playing tricks, the difference between the two locos is quite apparent when you do this:
I simply dragged a sampled area of both locos over to the other loco. The HST power car is lighter!
The vessel is most forgivable is presumably they had to fine a marine grade variant of the paints to work with? I'm guessing these were published as guides?
All of this is sort of why I thought BR Rail Blue was a colour recipe that various depots used, and why I'm surprised to see 'BR Rail Blue' cited without reference to some sort of more clearly defined colour standard when discussed online. There
is a colour BS381C 114 'Rail Blue' that might do the job?
Again, various websites reproduce this colour differently. Frustrating as a standard colour should transfer right over to HEX, RGB values, etc, and the colour should therefore be the same each time! Not much point having a standard with wiggle room built in.
On a slight tangent, I once had to produce a map of general election results (I work in that world as part of my day job, hence my anally retentive approach to colours amply demonstrated in this thread). I had to find out which shade of red Labour use. Their literature cited an RGB code for the official shade of red, yet the red in the literature sampled as a different shade of red entirely. How does that happen? They even used a Pantone colour!
Not a political dig, just me being slightly bemused!
I once had Halfords mix me two cans of a colour I was looking for. The poor guy at the paint counter was flummoxed when I asked for a BS 381c colour but was happy to mix me a RAL colour instead, oddly enough. He then went to his work station and mixed my colour from standard pigments. I guess even using this approach there is a chance that the base white paint he used was slightly off-white one way or another.