Catalina used Watco's Teak Oil (can get at Home Depot) up until about 1990 for the interior finish, after that they switched to a lighter color, water based varnish. Here's a direct quote from Catalina:
The varnish is Target Coatings-Oxford, semi gloss. If your boat is oiled it is Watco teak oil.
~ Gerry Douglas
If you have an oil finish, you can lightly sand (careful with the veneer) to get a more uniform appearance and then apply some Teak Oil, which will darken it some. In good areas, just clean the teak with some citrus based cleaner and then oil. You can also expirement with lemon oil which will not darken the teak as much, maybe one coat of Teak Oil to get a uniform appearance and then go with lemon oil from there.
On my boat, I sanded the galley and nav station teak back to bare wood as they were pretty mottled and did 3 coats of Teak Oil, looks great. The rest is in good shape, the plan is to touch up a couple places with Teak Oil and then use lemon oil.