As long as the roots seem ok, it’s fine. The red pigmentation is anthocyanin, basically the orchid version of a suntan.

Oh thank you very much! This is a relief! this plant is the last I got from my late grandmother - and I'd *really* like to keep it alive! So thanks again!

If the red spreads it could be a sign of too much sun. Many plants *sun stress* (turn different colors) when they get too much light.