Some patchy reddening is not that unusual, but if all the leaves have turned red, there might be a problem. Check the rootball - turn the plant out of its pot and see a) how dry it is or isn't and b) is it rootbound with very little soil in evidence. I suspect it needs potting up or planting out into the soil. It may be that the leaves drop, but if you can plant it out, it should recover.

Excellent. Many thanks, I'll investigate.

the only one I can find grows to about fifteen feet, tha is the leatherleaf mahonia or mahonia bealei , that has some leaves that are red, but also the center of the leaves are eferesance in march, and this week it is plant of the week

The mahonias that grow wild around here all turn red in the autumn. They look lovely.

We have a variety here that does this in the winter, its Mahonia aquifolium atropurpureum, and the aquifolium varieties generally take on reddish tints, sometimes whole leaves turning red. I'm assuming, though, that Andfos's plant isn't that, as this is the first year it's done it.

The leaves of mahonia japonica also take on red tints

Yes - but they don't all turn red all over, or is that your experience, Andrew, that they go completely red?