Christmas-ifying seafood linguine

You could use fresh chopped green herbs and some minced red pepper as a Christmas color themed garnish.

Make it a red&green linguini?

There are a number of ways to color pasta, or sauce - some might be natural, some might be commercially available. Like using spinach and tomato flavored past, or one could use food dye, or modify the sauce recipe (which can start out ranging from marinara red to pesto green to white sauce, depending on recipe), or add or modify toppings (flakes of red n green bell peppers, or tomato or broccoli, etc).

It might even work with just one modification, ie, green and white, red and white, green and red, are all Christmas-ish color combos.

I don't know what your recipe is, or what colors might already be present (based on ingredients, etc) but it might not be too tricky a change with a bit of planning.

We might need to know where you live & what you can get hold of at the last minute.

I'd say if you live inside 45° of the Equator, or South of it - ie, it's likely to be warm even if not actually sunny, you could possibly get away with some quick last-minute trimmings - a holly leaf, a gingerbread reindeer... anything you can find at the local supermarket.

If you live North of that, anywhere people wouldn't consider snow at Xmas to be outside the realms of possibility (even if it only actually happens once a decade) the I think you may have mistaken the word 'conservative' for 'traditional' & have an uphill struggle, which I'm tempted to think could only be cured by turning your linguine into a starter & setting up something with at least a sprout, a carrot & hopefully some kind of potato next to it for main.

At worst, grab a slice of turkey breast & turn it into turkey & seafood linguine.