Description
Highlights spells (in the spell book) that are missing from your action bars.
It also helps remembering to switch spells to their highest ranks, since they will glow in the spellbook if the ones on your bars have a lower ran

For it to work properly with spells that have ranks, please make sure to keep the option to show all the ranks turned off. I know it's not ideal, I'm sorry...

LIMITED SUPPORT FOR VANILLA FOR NOW - I tagged it as compatible with Vanilla as of 0.1.1b because the addon itself works and there's no reason not to make it available, but I'll need to rely on users to mention if spells are correctly highlighted or not as I don't currently play Vanilla :).

- If a spell isn't getting highlighted, please verify all of your hidden action bars before reporting, because they also count.

- Spells inside MACROS aren't going to be detected as being "on your bars", so they will still get highlighted.

Option to restrict what is highlighted
There is an option to hide some extra things (such as professions, or spells that are already on a stance bar) to prevent them from glowing for no reason.
Enabling this option (located at the top of the spell book) will remove the highlights from the following:

Professions (& their spells, except for [Lifeblood])
Auto Attack
Stances (Warrior/Rogue)
Forms (Druid/Shaman/Priest)
Presences (Death Knight)
Auras (Paladin)

Note: Some passives don't have the "Passive" tag in the spell book and will show the rank instead, which could mistakenly highlight it. Please let me know if something that shouldn't be highlighted gets highlighted, I will gladly update it ASAP! I don't play every class, so your input helps immensely! :)

Screenshot

Spellbook Highlight (Glow in spell book if missing from action bars)