I'm the type of person that would look at a formal display and take it apart one piece at a time. The art of formal display in the bonsai is huge especially in Japan. The style of the tree, style of the stand, type of stand, material of the stand, color of the stand, the color and shape of the main pot, the color and shape of the accent, the stand of the accent, etc... All play a role is giving our trees the best possible lime light.
Accents plants or plantings have always played a central role in complementing the main tree and tell a story of the current season. We are cursed in Southern California for having very little seasonal weather. This gives us all a false idea what the season truly is. I'm not staying it’s a bad thing but, something uniquely Southern California or areas where they see no drastic seasonal weather.
Now when you look at our accent plantings they all fall within the same range of plants thought out the year. Again, not a bad thing for keeping them alive in those tiny pots in 100+ degree weather but, doesn't help tell that complete story. Which is probably why our accent pot, accent stand, accent style plays such a pivotal role. I admire presenters of formal display that follow that traditional rule is awesome. You probably know they grew that accent for that particular tree only for particular show season.
From Bonsai Empire Website about accent plants : http://www.bonsaiempire.com/origin/related-arts/accent-plants
Season, the accent plant should resemble the current season. This means the color of leafs and the presence of fruits or flowers is of great importance.
Style of Bonsai, trees that resemble a struggle to survive (like a windswept or a growing in a rock styled tree) should be accompanied by a not too luxuriantly growing accent plant. Taller styles, like the literati, can be displayed with a tall grass variety.
Contrast, Bonsai trees with flowers or fruits should be contrasted by non-flowering accent plants, and vice-versa.
Origins, when combining several plants to create an accent plant, make sure these come from similar origins.
Pots, companion plantings can be placed in small glazed or unglazed pots, but also on a tile or slate. In the latter case, moss should be grown around the soil to create a mature looking plant.
Here are some of the very cool accent plants i have seen throughout this year. I really enjoy people that put as much effort into their accent as into their trees. It shows that they really have that eye for that fine detail no one will ever be looking for:
This one was my accent plant for a winter silheouette show. Not to winter looking there! Sad I know, maybe one day I can play with the big dogs!