Questions about Gouache Painting Outdoors

People had some good questions about my recent YouTube video Sketching an Old Firehouse (Big Revisions to the Painting Halfway Through)

sofachange "I recently tried gouache for the first time (inspired by your videos). I am curious why you started the buildings transparently when I would have expected you to go straight to opaque, which you did with the sky. Is there a rule of thumb to follow?"
James Gurney: I never paint the same way twice, but there are some general principles about what I do first and what comes later: 

1. From wet application first to drybrush later

2. Big areas to small shapes

3. Large relationships of tones first, accents last.

Eyal Dror "Timex weekender watch?"

James Gurney No, it's a $5 watch I picked up at a big box craft store. I wanted something with simple, clear numbers.

Chris Ma "How you arrange the colour scheme of a painting? How do you design the colours so that the painting is more coherent?"

Gurney: I've found the best way to achieve a unified, coherent color scheme is to use fewer colors, either by premixing batches of colors (which works best in oil paints), or by limiting the number of colors you squeeze on the palette. The second thing is that I try to capture the colors I see. Nature's colors are nearly always interesting and coherent.

Welther47 "I have a question about casein and acrylic gouache; won't they ruin the brushes when they dry or do you have enough time to clean them? Also, is there an easy way to clean them. I imagine Acrylic gouache will create a layer of plastic on the brush that will never come off again."

James Gurney You're right. Acrylic gouache will wreck brushes if you let it dry in them. That's one of the reasons I don't like to paint with them on location. I can't always get to a place to wash them thoroughly. Casein is a little more forgiving if you wait a few hours to wash your brushes because the emulsion takes a while to set up. Either way, I generally just use them for underpainting or priming, which I do in the studio in advance of the outdoor painting session.

biologicalparkinglot  "How do you paint reflection in water? I have seen you paint the ocean and rivers/creeks, but I am interested in knowing how do you paint objects reflected in water, such as in a pool or fountain, since it has been really challenging to try and recreate the effects of ripples and the movement of water while preserving the shapes or shadows of an object being reflected on it."
Gurney: I have a three part blog series on water reflections starting here.