I've just been to Decathlon and bought a black pair of hiking trousers, £12.99.
I already own two fawn coloured pairs, they then cost £7.99 a pair.
When I next hike I'll take a fawn and a black pair with me, just to ensure I don't get muddled as to which ones I wore on previous days.
I really like them, lightweight and so hard wearing, fits me like a glove and so easy to wash and so easy to dry.