OK...ordered some more T10 & T5 blue LED's from ebay seller -
zeropointelectronics - and once again received them quickly. Pretty easy job to replace the gauge bulbs - just removed the center console and the radio bezel, pulled out the three gauge cluster and replaced the red T10 filament bulbs with the new T10 blue led's. Fitted everything back in and ...

Looked pretty good, but the HVAC lighting now looked a very bright red by comparison. I also noticed that the blue part of the temp adjustment wasn't lighting up much. So next day, I decided to take it all apart again and take a look at the HVAC bulbs.
To get to these you need to take off the HVAC face plate and to get to that you need to pull out the HVAC so that can get to some clips. To pull the HVAC, there's metal clips either side that need to be compressed ...

I found this rusty piece of metal was the perfect shape! ...


The HVAC won't pull out far due to cables attached, but far enough to get to the retaining clips (two top & two bottom) that need to be lifted so that they don't snap off. First remove the three dial knobs and one vent knob, then lift these clips carefully and pull the fascia forward. I didn't get a photo of this in place but these are the clips ...

Once the fascia is off, the bulbs are revealed, and I realised why the lighting had looked so red. I'd forgotten that I'd replaced the clear bulbs with red filaments when I first got the car ...


OK, so go through my trusty box of spare bulbs to find a couple of clear T5's ...

I used a small pair of pliers to pull out and replace the bulbs ...

Once I had checked that everything was working correctly, fitted it all back together again, covered the cab with some sheets to darken it inside a little and ...

... now the HVAC has an amber glow rather than bright red and it matches in nicely with all the instrument needles and the radio. The "cold" blue section of the temp dial now lights up well, even with this much ambient light.
Really happy with the results.