TMI WTF

This is so gross to me. I was brushing my teeth and there was this green/brownish stuff on my tongue that was very difficult to get off. I have good dental hygiene. I have no clue what this is, but since it’s different to me, it’s mildly concerning.

I brush 2-3x daily, tongue included.

I don’t drink coffee, occasionally tea, but that’s less than once a month.

No soda/pop.

I am a smoker, 5-10 cigarettes a day.

Any ideas?