There is no ground rule for colours or prints that could do well for skirts. The occasion that you want to wear skirt to, always dictates the prints and colours.

For Office Wear- Conservative colours such as pastels navy, brown, black,ecru and white are preferred. Pinstripes are also considered formal wear. Team office wear skirts with fitted shirts for a serious, `don`t mess with me` look or , for a more related look, team it with loose fitting, self textured blouses , or blouses with small prints. Small heeled closed shoes work the best for the office wear; stick to neutral colours for footwear such as beige, brown, black or white. High heels can best left to be worn for after office dance parties. Avoid wearing heavy jewelry; a string of pearls and ear studs or small earings convey a look of professionalism. The lengths most suitable for a formal skirt is knee and below for summers, you could wear a knee length skirt, however, for winter, you could wear a long skirt.

A strictly office wear skirt can be converted to a party skirt in a question of seconds, by just altering the things that you wear it with. Wear a nice floral juted top, add some colour to your lips and cheeks and throw the string of pearls and the small heels in the locker, to be replaced by some fun trinkets and neck wear.
For more casual outing, bolder colours and prints which are `in fashion` are preferred. Colours such as fushia pink, raspberry red, lemon yellow are all perfectly acceptable, however, ensure that you accessorize right and team it with the right top. One could have an array of prints in vogue for a season, such as large floral prints, ditsy prints; border prints, paisleys, geometric prints, etc. And all of these goes perfectly well for a start. Team a solid colour top with a skirt having large prints. Teaming tops and skirts, both with large prints could prove to be a fashion disaster, so avoid at all cost.

Additionally, all skirt length from thigh to ankle are worn and work well for casual wear. The shirts could be more stylish though, from sleeveless to full sleeves,  From bright colours to neutral prints, everything works.
Finally, the key is to create a balance look; if the top is highly of the ensemble, is to keep the skirt and jewelry basic; likewise, if the jewelry is loud and creates a statement, keep the top and the skirt basic.