A bright shade of blue or a bright white would be nice and bright. Gray would match the roof.

white trim and railings. Grey background, Blue or red doors.

Is the red tape (or whatever it is) around the lower left window to see how beefier trim would look around the windows? If so, than I think that is a good idea to enhance the window trim.

I'm not a fan of the current siding color (gray). It looks dingy to me and unappealing in its current color. There are cleaner, more modern grays. I do like the blue trim you are trying out on the beam area - if you can get proper coverage. Right now it looks a little like a test strip. IMO if your railings are painted black, rather than a trim color, they will disappear which will make your building facade less busy. If you do paint the trim a contrasting color, paint the doors the same color.

Overall though - the advice to go with a commercial designer is spot on - there are marketing colors designed to attract and others that will unknowingly repel customers.

Light gray siding, darker blue trim and limited amounts of dark red accents would be nice. White siding would work as well.

If you do not want to hire a commercial designer perhaps knowing where the building is can help with suggestions. Certain colors look different in different lights. If these are not longer term renters perhaps something lighter to invite people to look. Something that someone mentioned elsewhere if that is plastic siding on the building dark paint could cause problems with it buckling. Scroll down to Jennifer Hogan's comment.

https://www.gardenweb.com/discussions/5882574/hold-the-cream-before-and-after-design-ideas#n=17

I would paint the siding a bright, clean white, and railing either gray, or blue. If cost is a concern, white paint may be cheaper than a tinted color paint.