A little more tinkering last night. Some of my LEDs have now been yellowed by putting a bit of yellow drinking straw over them! Enough of the light gets through, but now it's more yellow, and it's easily reversible in case I need to replace the LED one day. The LEDs themselves aren't visible, so neither is the yellow plastic covering them.
I then turned my attention to the corner of the layout where the signal box is. It was feeling a bit bare, so out came the clump foliage! It's cheap stuff, nowhere near as nice as 'proper' Woodland Scenics stuff, but it's convincing enough. My technique, in case anyone's interested, is to lay a foundation of neat PVA glue down first, and then gently position clumps of the foliage on top. Of course it's not going to hold its position until the glue is dried, but it means there will be a good grip on the bottom. Then, to stop it from falling apart over time, I drizzle watered down PVA over the top, as if I were ballasting. The foliage soaks it up nicely, meaning that bits are less likely to break off. It also gives me an opportunity to gently sprinkle just a little scatter grass over the top, which just adds a little colour variation. I've left enough space for some signal box stairs, when I eventually get round to making some. I'd need some grass there too, where there aren't any bushes.
Seeing as the clump foliage packet was out, I thought I'd have a go at sprucing up my platforms. Heritage railway platforms do tend to be festooned with brightly coloured hanging baskets and planters! I ended up making some little plant pots out of a black drinking straw, with a pinch of clump foliage stuffed in the top. They work quite well, I think. I may go back with a fine brush and paint some flowers onto them when I get a chance. Apologies for the out-of-focus gentleman on the platform; he'll need to see a doctor about that one day.