Original art needs protection, and a custom frame with a glass or acrylic front is perfect for this. However, the wrong frame can draw too much attention away from the art. So, framing something isn't just a matter of finding a frame and throwing the artwork inside it. You have to choose something that can enhance the art, or at the very least, ensure that viewers' eyes don't wander to the edge of the frame, rather than the centre of the art.
Subtle Colours That Blend With the Background
One good choice is a colour that is subtle, neutral, and well-blended with the background colours of the artwork. Even if you have a white mat separating the art from the frame, using a neutral colour that matches a background colour in the art is a nice, unobtrusive choice. For example, if you have artwork of a forest with partly cloudy blue skies and light-coloured wood, a frame that matches one of the background wood shades or an ivory shade that's also in some of the clouds could be an excellent choice. It's so light and neutral that it just fades into the visual background.
Generic Colours That You Just Don't Think About
A similar option is to use a generic frame colour that no one will really think about. Gold, silver, and dark and light brown are all common, and people usually see those colours in frames and just don't think about them much. Unless you choose a huge, thick frame, those colours will not really grab people's attention.
You can also use frameless frames, the acrylic-box styles that don't have a traditional outer frame. The point of this option is just to have something that allows you to handle the art without damaging it.
A Minor Colour You Want to Emphasise
One more option is to find a colour in the art that isn't too common throughout the work and find a frame in that colour. This works best for avant-garde art that you don't want to stick in a plain acrylic box. Normally, calling out a bright colour by having the frame in that same colour could overwhelm the art, but for more experimental items, it could be the right finishing touch. Think of the cartoonish Lichtenstein-style pop art from the 1960s or the abstract works of Jackson Pollock; those could work with stark, black frames or frames with matching bright colours.
The right frame for one piece of art isn't going to be the right frame for another, even if the colours in the art are similar. It's best to contact original art framing services to learn more about which specific frame goes best with that specific piece of art.