I'm working on a game idea that involves having a deck with 7 ranks and 7 suits, where both have clear orderings. (The classic western card deck has 13 ranks which are ordered and 4 suits which are usually not.) I thought of the classic 7 "ROYGBIV" colors, so I wanted to come up with symbols that would go with those colors and also be clearly ordered even if you couldn't see the colors (for color-blind people).
I think the symbols I came up with work very well for this purpose. Each symbol has one more corner than the previous one.
| Red Balls. 0 corners. |
| Orange Flames. 1 corner. |
| Yellow Lemons. 2 corners. |
| Green Trees. 3 corners. |
| Blue Ice. 4 corners. |
| Indigo Crystals. 5 corners. |
| Violet Flowers. 6 corners. |