The yellow colouring, or variation, is natural for a mature Umbrella plant. The more light it gets the more green it will become.

You can certainly trim it down to size - it will make the plant thicker. I have seen Umbrella plants as standards (so all the leaves trimmed from stem with lots on top like a lollipop) or like yours - tall and thin.

If you can stand it, I'd wait till spring before chopping it back though - and if you want an extra plant, reduce the bit you've chopped of to about 4 inches of stem, or two sets of leaves with a bit of bare stem at the base, pop it in a bottle of water on a windowsill, keep it topped up and in about six weeks, roots will have formed and you'll have another plant.

In south america these plants are currently in their 'summer' growth stage. So depending on how cool/warm it is in its current location will determine when and how to cut it down. I would expect lower leaves to be dying off to allow for its continued growth at the top end. When you cut it down expect the sides to get bushy. As kildemorie says you can train these to become lollipops or standards if wished. If you don't want it to bush out at the sides, just trim back the leaf side shoots when you cut the top out.
Your local garden centre may have advice on feeds.

Given you live in the UK, I stand by my advice above, despite Avkg47's extra info - I've had a plain green one of these plants for over 30 years - the one I've got now isn't the original, because when they get too tall, I've always done as described above (in spring) and then potted up and kept the new plant and given away the parent.
I have to say though, looking at the pic again, it looks like one I bought in Ikea a few years ago - it grew straight like yours, and although I cut it to try to get it to bush out, it didn't - it just continued growing straight up. And lost leaves at the base the taller it got. Gave it to my sister in the end, who needed a tall, narrow plant...

It depends on the 'umbrella plant' you have ... darmera peltata will not produce a show of flowers if you cut it back early in the spring - so cut back after flowering; schefflera, as far as i am aware, does not flower but reproduces in the tropics via layering. When layering is stopped for both these plants, then the base plant will eventually die off. They are short-lived conservatory plants in this country. If you keep potting on the 'babies' you will always have a plant in your conservatory - but you need to keep it up!!

I don't know where the info on Schefflera you mention comes from Avkg47, but I disagree - the plant pictured here would once have been called Heptapleurum arboricola and is now reclassified as Schefflera arboricola. It is a houseplant in the UK, not a conservatory plant, and does not appreciate temperatures over 70 deg. F. Even Schefflera actinophylla is the same, not liking temps over 70 deg., so again a houseplant. Neither is short lived either - I know someone who donated theirs to an old folk's home because it had got up to her ceiling (10 feet) and was over 6 feet wide and 22 years old. They generally do not produce aerial roots when grown as houseplants here either. Certainly, I've never seen any on mine, and there were none on the 22 years old one either. You also refer to the 'babies' - it doesn't produce babies except in its natural habitat. It's also a very good subject for bonsai, and tolerates a fair bit of neglect, so all round, very good houseplant here.

Darmera peltata is, as far as I know, never grown as a houseplant here, it being a hardy perennial outside.

I just cut one in half this summer. The cut off bit is growing away nicely in a new pot, and the bottom bit is also all right. Not branching out yet, but I am hopeful.
Good luck with yours :o)

Thank you Bamboo - my info came from some rather old RHS books I have inherited from my father, in which flowers for the Schefflera are not mentioned, but aerial roots, even as a house/conservatory plant are, and include pictures of potted samples with the aerial layering roots I mentioned. High warmth and high humidity are also mentioned, to reproduce their natural environment, which would result in off-shoots, ie babies, for planting on. Also, a warm, light and humid conservatory is no different to the same indoors - as I said in my original comment; the plant will respond depending on the temperature etc in its current location. Perhaps too much information provided to the question?!!

Hmm, well that's certainly not anything like up to date information, sounds like it came from the days when the plant first started being grown over here, and when they would have made some attempt to mimic its natural growing conditions, believing it wouldn't cope otherwise.
My info is from a modern Houseplant Book by D. G. Hessayon - and having grown it myself for years and years, I know how it behaves. It's a really resilient and useful houseplant.

https://scontent-lht6-1.xx.fbcdn.net/v/t1.0-9/16142216_10154340998633063_8121672194315831835_n.jpg?oh=c8b2d856fe76f48acae1609b5ead0a20&oe=590AFF48

I've tried to paste a pic of mine, not sure it works. I've had mine for over 30 years and it occasionally gets yellow leaves at the bottom that fall off, not too sure whether it is when it has dried out too much but it doesn't seem to suffer much from that. Mine is exactly like the one in your pic it does not produce flowers or babies. I haven't trimmed mine down at all it just grew side shoots naturally but it is getting a bit big and maybe I should try cutting it back a bit.

Interesting information. The Umbrella plant or Schefflera is popular for outdoor hedges here in sunny Florida where temperatures are well into the 90s. Its a very resilient plant indeed, and certainly not just a houseplant.