As the appearance of the garden has a modernist style with the straight lines and concrete furniture how about a Mondrian influence and add a bold strip of blue? It is a pond and with the right shade it could look really relaxed and contemporary. My daughter's suggestion is a chalky lilac!

I love it! I agree with paint color. Too much purple in there. How about something that will complement the warm brown of the leather furniture? I think the paint you have right now would look good with a more modern design scheme with light furniture which probably isn't in your budget. Paint is cheap to buy. Get some paint swatches and hold them next to the floor and leather sofa. It will help you see what looks good. Pottery Barn colors from Benjamin Moore paints are pretty fool proof.

I think the first layout is fine. You might want to consider moving the door for the storage room of the master bedroom so that it opens into the hall. That way the kids can use it for overflow storage. Also, that hallway is big enough that I think it could hold a large armour, providing more closet space. (There's no need to sleep in the same room as your clothes, so long as they're not too far off.) Also, don't forget that while the drawing shows kids in double beds, this need not be the case, so there will be more room for furniture (dressers or whatever) in their rooms. Finally, that step to bedroom 4 will not be odd at all. I've seen it in other homes. It looks clumsy in the drawing but it isn't. What you'll see when you come up the stairs is a bedroom door on a slight diagonal. It's only an odd jagged step if you walk like a robot, in straight lines along the wall, which is what your eye is doing on the drawing but you won't do in real life.

Deep gray and all the other accents in silvery old wood and cream. This will add drama, allow the other elements to bring ion light and set off the concrete wall as a true feature. If you want light instead of drama, then go for a very pale beige stone. It will echo stone colours in both the concrete and rocks...