I was writing a song in Bbm key. And the chord progression goes something like. Bbm,GbM7, DbM7/F
In this situation does the GbM7 going to DbM7/F also consider as chromatic progression ?
If it is,why ?
"Chromatic" suggests that what you're describing involves pitches outside of the key. The pitches of your two chords—G♭ B♭ D♭ F followed by D♭ F A♭—are all included in B♭ minor. Thus there are no pitches outside the key, and thus it wouldn't be considered chromatic. Instead, we call it diatonic, which is the opposite of chromatic.
To give you a visual representation, we can also say that "chromatic" suggests the use of accidentals. Let's look at these two chords in the context of B♭ minor:
Since there are no accidentals outside of the key signature, we would not call this chromatic.
'Chromatic' has a very simple definition - 'using notes outside the scale of the current key'. If you're using a key signature it's chromatic if accidentals occur, it isn't if they don't. (Let's dodge the issue of harmonic minor scales for now!) I think you may have invented a different definition of 'chromatic'?