What colours are acceptable to be worn at a funeral?

It depends on what those closest to the bereaved want. In the absence of any specific guidance, I would go for sombre colours, but not necessarily black. Some people specify bright colours for a funeral, especially following the death or a child. I've never been to a funeral though.

Grieving and grievance are not the same thing.

I don't think people in the US necessarily follow rules about funeral attire all that closely. Probably mostly dark or subdued colors, but in some cases, people might wear bright colors or just wear whatever they want, because either that's how they do things, or it's what they think the deceased person would have wanted. I personally think it's fine to wear whatever you think is appropriate.

A dark color..

Any color one wants to. These rules are old-fashioned. The dead don't care what you wear. People wear black stuff to fit in with a very old custom.

Dark & neutral I guess .......... though I just attended a memorial service (the British Consulate in Montego bay was killed) and wore a French Blue shirt,+ complimentary ties, Pressed light colored Khakis and loafers ...........it was too hot to wear anything else, but this is Jamaica

For me personally, black.

I don't know, but a wise man once said don't wear black to a funeral.

I always wear a light pastel at funerals. Black is just so affected!

Hey put the "fun" back in Funeral... Wear bright colors, laugh, have a good time, celebrate...

I always look good in black.

Depends on the customs of the person being laid to rest. If it's a funeral for a Japanese (and some other oriental cultures) person, white is the way to go. I believe there are one or two Oriental cultures who favor red as funeral wear also, but don't quote me on that. My memory has never been as good as it used to be.

In my culture, it is customary to dress formally for funerals and to wear drab, muted colours. The immediate family of the deceased will often dress entirely in black.

I suppose if you wear what you normally wear what difference does it make? As long as you are clean and neat, I think the word "respectful" fits.