From the start Natsu told that he can use Igneel's power only once.Flame Dragon King spells are just normal Fire DS spells which have more intense flames. These flames were copied from Igneel, and acquired in essentially the same fashion as LFD.
I think this is true, at least from a story telling perspective Hiro would go out of his way to make sure we know.
To be honest, the tattoo's themselves are a bit confusing. Gray for example has a tattoo when he uses DeSM (vs Invel), yet he didn't in Hargeon. One could argue Gray is using Silvers MP whenever he sports the tattoo, I guess.
And in the last part of chapter 465 Natsu told Happy to leave him as "Igneel's power is about to vanish soon enough".