Colour- is one colour best?

I would stick to one colour when introducing them. I would add a different colour if the difference meant something, for example using the part whole model to show the link between addition and subtraction. I also use two colours to show number bonds in a ten frame or in the dot numbers.I like the reversible ones, because then you can show how they all go together to make one number and change the colours to signify different number bonds for the same number.

I tend to use simple one colour to avoid visual confusion and ,as you say Judy, distractions - when introducing a new concept However, I fairly recently moved from one colour Base 10 equipment to 3 for place value simply because some of my pupils have equipment at home and these were cheaper and faster for them to get online. So that I could 'mirror' this (particularly online) I use the same set and am a convert. It seems to work well to initially use different colour blocks for the hundreds 10's and units concretely. If we replicate this, pictorially, in a book, it is one colour however and I would fully expect that a student could use any / one colour concrete materials to the same effect though as their skills develop.

I use double sided/two colour counters for the patterns when we start working on the components so that again, they can split the pattern into components and better visualise and then describe.

I have occasionally used different coloured pens for introducing formal addition in columns , only if a pupil has had a real difficulty in 'lining' up the numbers properly (but did understand place value).

There seems to be a lot multi-coloured fraction materials which is really nice for equivalency etc. but when introducing, for example improper to mixed numbers, I would want all my 'parts' to be one colour. (if that makes sense).

Generally, I'm a fan of keeping it really simple visually at least initially.