Paul, the bulbs in my car are already blue. The thing is, when they light up, the blue mixes with the yellowish tint that's already present in the dashboard face and you end up with the greenish color that we all see. I think.

As for replacing the bulbs, it's a pretty simple job for all of the bulbs. For the ones behind the dash, you have to pull out the instrument cluster. That's easily done by prying up the little plastic tabs. (One of them says "unleaded fuel only, just pry that off, and the other one is blank)

Behind those tabs are screws. There should be 2 total. Unscrew it and pull the dash out. That's it. If you've never pulled the dash out before, there will be tie wraps behind it holding it in place. You might want to clip those, no big deal. Just be careful of the wires. There ya go.

As for the other bulbs that aren't part of your instrument cluster, the dash panels pry off easily and you can replace the bulbs just by doing some prying at the edges.
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Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'