Runes grant magical abilities. Rune artwork is representative of its abilities, whereas the artwork of the three abilities combine to form the rune.
When equipping a rune, rune artwork displays on the user interface. When a runic ability is activated, the artwork of that specific ability is highlighted and not the entire rune.
Will all spell types (bolts, shock, shouts, fields, etc) have similar art? For example, if Rune Ability 1 (from above image) is Fire Bolt, will Water Bolt have similar art? Perhaps. Perhaps not.