What colour are mountains? Green, right? Or brown, or grey, or black. Or sometimes, on the horizon, an indefinable blue. Except in August, that is, when a blaze of purple rushes over the lower slopes. First to get its colour out is bog-loving cross-leaved heath, with its rounder, pinker, bell-shaped blooms; then comes bell heather, with its vivid fuchsia flowers; then paler, but abundant ling. For a brief time, heathland is transformed and the view is breathtaking. Smaller hills are entirely carpeted in purple, waves of lilac lapping up against high peaks. Within a week or two, it fades to brown. So make the most of the fading season’s golden light, grab a bivvy bag and your camera, and spend an evening watching summer’s glorious finale. Anywhere hilly is likely…