What colour thread?
 

I enjoy doing paper piecing designs and when I quilt I almost want it to be ‘invisible’ and for structure and texture only. These designs can be very multicoloured so I’m never sure what thread to use. What thread would you use?

You could use invisible (clear) thread. This would seem to suit your need best.

With regular thread I place strands of the different threads on the various fabrics to try to pick the best one for that quilt; there isn't one color that works best with all quilts. And for some quilts it's just not possible to find anything "in the middle" (like, say a black and white quilt).

I have some invisible thread - I think it is made of nylon or similar. Is this ok to put in sewing machines then? I have only been machine sewing 7 months so still a lot to learn!

I haven't use it enough to be anywhere near an expert on it, but I'll give you what I know. It would be either nylon or polyester, and you can use regular cotton thread in the bobbin. There can be problems with invisible thread tangling or breaking, so you may have to experiment with (lower) tension and different needles to use it successfully. Definitely try it on scrap material before using it on your quilt.

Polyester threads can be very invisible and easy to work with. I like Bottom Line thread by Superior in a gray or beige color.

I have used and I am using this thread right now with great success. You will have to adjust your tension until you get what you like. I have two machines, and one of them handles this thread better than the other. I normally use a regular thread in the bobbin. Make sure you have a piece to practice on before hand.

Thread weight makes more of a difference than color. Invisible monofilament thread like Superior's Monopoly (a polyester), Filtec Essence (Nylon) and YLI Invisible thread (also a nylon)would do what you are asking but they can be fussy and lead to frustration. Do experiment with them because it would benefit you to be able to take advantage of these threads when the need arises. Edited to add, some people have found they need to use a thread net with these threads. I do when I use the big cones on my LA but I have a tiny cone for domestic machine use that I put on my large cone holder for my domestic machine and have had no issues. I believe that one is YLI. I use Essence and Monopoly on my longarm. All monofilament threads do have a certain amount of shine to them and are not 100% invisible.
Threads that are more user friendly and don't show much (texture rather that quilting stitches) are super fine threads like Wonderfil brand Invisifil which is a 100 wt polyester. Superior also makes one called Microquilter. I prefer Invisifil but that is just me. Here is an example of a quilt done with all Invisifil. https://www.quiltingboard.com/pictur...t-t221823.html
Silk thread will also show texture. Just google images of Diane Gaudynski to see examples.
As far as color, well that all depends on the value and colors in the quilt. If you use a lot of high contrast value (light and dark) or brights there will be places where the thread will show more than other places no matter what you use. It has been my experience that sage green, a greenish gray and golden tan seem to play nicely with everything.

I use gray for most of my piecing, unless it is mostly whites, then white, or mostly black, then black. The gray seems to blend in with most everything. Just MHO.

Thanks feline fanatic - that is very helpful. It is for things like this that I am thinking about quilting. As you can see colour is tricky!

https://www.quiltingboard.com/pictur...s-t298704.html

I think the 100wt is something that I will explore further so thanks!

Oh RJ, I just went and peeked at your Christmas block. Wow, what a lot of work that must have been. If I invested that much time and effort into the piecing I would do the same for the quilting. I would change thread colors to match where you want it, rather than trying to find one color to do the whole thing. The beauty of silk and 100wt is that you don't have to be exact. You could use one shade of green for all the different greens, same for the blues, reds, etc.
This project would also allow you the opportunity to embellish with threads like using a metallic on the Christmas tree garland, star and the candle flame.
But if your intent is to ditch the main elements and leave the quilting at that, then I think you will do fine with either an invisible monofilament or a neutral color of a 100wt like Invisifil or silk. I hope you can find it in the UK.