Not sure where I came across this tip, may have been a podcast or an interview I read, but it seemed like a really useful one for me.

At the moment, I struggle managing to get sketches completed if I am drawing outdoors on the train or in a cafe for example so trying to remember or add in colour always gets missed.

Simply writing notes on the sketch, be it light direction, colours, textures etc will be so useful going forward for me. Will also free me of trying to get exact matches and just go with blue etc. but I can also make notes on where highlights, midtones and shadows go.