Don't get me started...

I, um, believe, Casavant, that what you are referring to is a 'trumpet celeste'?

Also @CharlesW many people get relative pitch off F# and Eb because F# is bright and Eb is rounder. F is a bit interesting because it is on the rounder side whilst being so close to F# also so perhaps you find the rounder pitches easier to memorise? I find F is a really good sort of turquoisey kind of flavour and Fa in chant has that similar colour emerging regardless of pitch sounding.

And @CHGiffen I knew it! You are a double reed player!!! From a bassoonist/baroque bassoonist to an oboeist my hat is off! Tim Tam slam that.

LOL Yes @MJacksonOsborn ha ha.
Of course.
Every person with synaesthesia is different. and YES pitch systems will change the roundness of notes etc.
And yes not every Eb will be round... but I somewhat think you are **** stirring here just to get this response, I think you know which A and which temperament I'm referring to here... assuming you are using that A and that temperament you can assume that Eb is rounder and F# is brighter or edgier. That isn't my own speculation, there is an American tutor of pitch memory (I have forgotten his name but he does a 90 day course) who bases his whole introduction to relative pitch on F# as the starting note for this very reason.

BTW fun fact - Lots of children who have watched The Lion King can sing the first note of The Lion King Circle of Life accurate to the pitch they heard when they saw it (so VHS might be a bit different to your DVD) even if they haven't watched it in a long time. I dunno why, but there is a thesis for someone who wants to work out how this pitch memory occurs. I reckon there is something in the link between emotional memory and the physical memory here... but I'd love to know what people think...

Synaesthesia can be a visual thing or aural when it comes to music. I'm more visual but sometimes aural though rarely.
Some people hear the tonic of a key as red and other people only hear C as red and other people might hear C to be Purple or some other colour. So yes, logic would say that these notes would change and for hearers of colour pitch they do (for some of my students they do) but mine is mostly visual so no matter the pitch system it seems to stay rather similar - some exceptions of course - a note within a chord will change colour sometimes based on relativity which tells me that I move a slight bit between moveable and fixed when singing motets which demand a certain tonality etc.

SO GENERALLY Visually
I see colours in the note heads for G, F, and C clef (no matter where placed on the stave) C is Red F is a turquoisy sort of colour etc. no matter what key we are in they remain the same. No matter the pitch system either these remain the same.
If the choir decide to transpose down a tone from what is written on the score however for some reason I can still see the notated C as red but I have to convert the C to a Bb and CAN attempt to change the colours with my brain if I think hard enough about it being Bb but then I just visualise a Bb on a page but that requires a lot of thinking - on good days I will think in moveable doh and this will be no problem because then I read it like chant but this is not always the case, sometimes I'm just in a fixed position here - it's not an excuse if I get it wrong, it depends on how much moveable/fixed I've sung at the time.
and in Chant (no idea why this is different btw I'm still discovering this for myself) but I see the notes as relative as though every doh is C and every Fa is F no matter what key it is sung in. So if doh is G in chant I will see the neume on doh in the colour Red exactly the same red as the C in the 5 line stave.

When writing theory I also see tonic function chords as Red, Dominant function as Blue, Extension of tonic as Green and the ambiguous other chord as orange, if a chord is a pivot chord it is purple. BUT THAT theory part is not synaesethesia - that part is memory I believe.

I think the reason is because I used fixed doh for 5 line stave notation and moveable doh for 4 line.

One of my kids has it for timbre, and another has it with numbers so he's great with harmonic progressions.

I've also named and recorded a pitch system after a priest that used to reliably go flat by the same increment - he does this in his speech too. His thirds tend to be similar to true thirds. I'm working on polishing it up.