There is as much artistry in the accent as there is in the primary plant (bonsai). The critical factor being what the display venue is. A crowded club exhibit is mainly for a veiwing public that get as much kick out of seeing a potted up pansy to exbiting in the National Toko Kazari display competition where the wrong accent can spell disaster.
As I said abov, the club scene is a no brainer as for the most part anything goes. Keeping it simple is always a bonus, but the public likes variety and it seems we are always eager to oblige.
The more professional display is a little different. I can offer my point of view based on displaying twice in the above venue as well as study with Larry and Nina Ragle, Hidecko Metaxis and Kathy Shaner.
The accent has much to do with helping set a few ideas for the display. It can be a seasonal marker or it can help convey where the display is taking place, (geographically). The importance of the accent is dependent on another emotional marker....the scroll.
If the scroll sets the season then the accent must help set a location. In the event a scroll is used a lot of attention must be paid to keeping redundency down to a minumum. If the scroll contains flowers or blooms then it may be more wise to look for a grass or non blooming sedum. If the scroll sets the season then the accent should also convey that season. In spring, a flowering accent may have a few buds and maybe one open flower. We are not looking for an accent with 12 flowers on it, since this would mean early summer. We want the accent to be subtle and allow us to see the buds and maybe one flower and imagining what the accent "may" look like in three weeks. To show it all so soon does not allow for imagination.
In fall the scroll may have migrating birds or a moon with clouds... in this case we may want an accent with brown dried grass dipicting fall and the end of the green for now.
In winter we may have narcissus bulbs breaking the surface or another winter blooming species.
In summer full lush grasses are appropriate or small clumps of bamboo or mondo grass. Rabbits foot fern makes a good summer plant for an area with water or a lowland diciduous tree display.
Keep in mind it is more important to match the plant to the geography than to match the plant to the area in which it came from. Meaning ferns that grow in Hawaii and no place else would still be good for dipicting that kind of area in California if it is the kind of plant that would grow there. Dipicting a high mountain semi arid desert scene with a rugged juniper and a fern from Hawaii would not work very well. But we might take that fern and the rugged juniper with a long waterfall scroll and depict that fall plunging into a canyon with ferns growing at it's base.
Sedums are very good for making accents since they can add a lot of texture to a display. Some bloom and some have good colors in the leaves. Keep in mind that while it may be tempting to mix several plants together to make a very interesting display of accent plants, this can ruin and muddy the display. The viewer needs to look at the display, gather the visual ques from scroll and accent and focus on the tree.
The club exhibitor will usually have a tree and accent. In this case there is much more freedom to play around the edges and experiment with the accent since there is no scroll to compete with it. Just make sure it is compact ( not a lot of trailing stuff over the pot) has some patina ( not potted up last night) and is subtle ( cut off some of those blooms!).
I will post some pictures of some that worked and some that didn't. (IMO)