I'm not a fan of backgrounds however I think I need one as I just setup a tank in front of the window. I'm not worried about algae but light. I have odd hours and want the fish to sleep sometime.

I'm having a hard time visioning what it might look like and was wondering what recommendations were for color? I'm thinking black but maybe blue is better? What's better for the fish? What looks best with lots of background plants?

Black.

I think it depends on the color of your substrate. With black sand I use a black background. With play sand or similarly light colors I use a dark blue.

This is what the substrate looks like.

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I like black for hiding things like filters, heater, etc. With light colors you can sometimes see the item plus a dark shadow from your lighting.
For a quick and pretty cheap test, you can get solid colored fabric to hang over the back for a while to give you a better feel for what you like.

Test with pretty much anything you have around the house:
Towel, curtain, poster board, construction paper (careful: colors run when it gets wet), garbage bag...

Anything, just to see what color looks best to your eye.

I was about to get some shiny black background paper from the LFS so I tried some construction paper to see if that's what I really wanted....4-5 months later and the construction paper is still there. No use in getting the nicer stuff when you can't tell the difference.

If you are into natural or semi-natural looking background, avoid blue. The only underwater environment I know of that has a blue look to it is the ocean. Most lakes and rivers tend to run green or brown and if the water is really clear, you still see a background of tans, browns, greens and black (shadowed areas). In the artificial aquaria world anything goes, lol, but personally, I think black has the most dramatic effect and does best for hiding equiptment. Some of the light diffusion screens used to replicate daytime skies in the Nature Aquaria is also very effective and beautiful, but, it won't hide anything!

I found some fabric that was black background with green fern fronds (several shades of green).
Looked pretty good as a background.
I also found similar shades of green in a marbled pattern (OK, not as good as the ferns) and a blue marbled pattern (looks good for the brackish water tank).

I use velcro to stick them to the tanks.
Sticky velcro sticks to the rim of the tank, but sticky does not stick so well to fabric, so I take a few stitches in it to make it more secure.

By the time the plants are large, the background is mostly hidden, and the few fern fronds that show look just fine.

I have other backgrounds, too. One has pictures of house plants that are not under water plants. Clear enough that I can ID the plants. It is odd... I see the house plants and think 'What is that doing under water?'.

Thanks for the comments, I'm never good at this stuff, I know what looks good when its together, visioning it before hand is difficult. I don't have any sheets or anything I can try, its 6ft long and just covering a small section doesn't cut it for me.

The tank came with a background that was double sided, I hung it up for now, I don't like it but I'll see how it looks when I get plants in there, if not I'll just go black.

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Mines dark blue fading up to light blue, looks quite good IMO, although i find putting backgrounds on painstakingly hard and stress full!

Had some brown packing paper in the last order. Taped it to the back and I am pleased overall. Try crumpling a brown bag and see how that looks.

i spray painted a piece of cardboard flat black for my tank.

Yeah I'm gonna go black, I also going to get some black substrate. I currently have just the soil laying in the tank and really like that look. (no water)

Only problem now is all the black sand has crap in it, I don't want any nutrients just plan sand or small gravel, preferably gravel.

I have a 45g 4ft tank running for 9-10 weeks now and plants are doing amazing, no ferts and I've had no algae, its been a dream, my LFS doesn't believe me. Now I worry if I get substrate with crap in it I'll get the algae outbreaks lots seem to experience with a new tank.

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Black is my favorite. A black background and then the glass getting covered in GSA makes for an intresting look.