it's generally not bad excepting the already mentioned overexposure. if you set your camera to manual exposure and just keep firing and re-adjusting you can end up at one that will eliminate the extra light (by higher shutter speed or closing the iris). though black backgrounds can result in dramatic images, if you are using flash I have discovered it is much more difficult for the auto exposure on a camera to meter properly even with spot metering. since the background is black the camera thinks it needs to pump out more light. if you can limit the light to a constant source and use manual exposure then you can take a range of pictures which you can see before taking, whether or not it will be too bright or not. hard to do with flash since you can't 'see' how much light the flash will have or tell if it's enough/too much while taking the picture.
you have to be careful mixing different light sources, because as I've found out taking pictures of our local orchid shows, you can end up having 'shadows' on the flowers/plants of different colors, which you won't be able to edit out of the picture and it will look funky. if you happened to look at pictures i've taken of flowers at our shows, you can often see funny colors here and there that are because there are portable halogen spot lights on tables, portable fluorescent and tungsten fixtures/bulbs mixed together pointing at the table in addition to the overhead tungsten lights in the ceiling at the nature center, in addition to natural light skylights over the room and the occasional flash that I might use on my camera. can end up with an odd mix of colors
also, if you move the camera to one side a little more, you can see more of the sides of the flower pouches, and if from above a little more you can see some of the detail of the inside of the pouches a little more and possibly some of the detail around the opening of the pouch (just thoughts)
