My Nexus 4 was stolen so I went for the 5 but I was hesitating between the black one and the red one. I hadn't seen any review of the red version so that's why I'll make one for the one who can't decide!
First of all, Google mention that the phone is bright red. And it is! Its very very bright and it's amazing.
When I opened the box, the phone dazzled me! It's very flashy and its like neon red, eletric verilion or orange red (See an approximation of the color in attached files).
It's true that it look a bit orange. But in a certain way, the color affects you depending the light there is. In daylight it looks very bright, but in a room with no natural light it will look softer. But it's still bright. You can't get lost with this phone, we can see you from far away (a bit like the red-orange security jacket but not that extreme of course )
I'm totally in love with this phone, i think it looks amazing. But be aware that it doesn't look like a "normal red phone"
Regarding the case, i wanted that the back can be seen, I didn't wanted to hide the color of the phone. But I think that the transparent cases from Spigen (Ultra Hybrid) and Ringke (Fusion) were too big and would ruin the Nexus 5 design. So I found on clubcase.fr an interesting case. It's thin and frosted, not fully transparent. It looks quite good (but not so sure about the protection it offers), it soften a bit the color but the phone looks a bit more orange or pink depending the light. But it isn't that disturbing. I also bought the Diztronic Voyeur case because it seems stronger, but it will come in a few days so I don't know how it will look like on my Nexus.
I hope I could help you in your choice
PS : I'll try to add pics of the phone as soon as possible
Edit : Here is the link to my imgur album with all the pictures with different angles : imgur. com/a/5rymn (remove the space before the dot)
I also have received my Diztronic voyeur case. It looks great and much more protective than my other case but it's a bit thicker (pics in the link above )