Have never heard/read that and that wasn't my experience back when I used to use regular color instead of henna . . . Not saying you didn't read something like that here - I probably never see 95% of the posts, LOL!
2C/3A/3B - mod. CG, med. to fine, normal to low porosity/normal elasticity
Current Main Rotation: MG217 medicated or Aim2Health 'poos as scalp needs, YTCarrots or Elucence cond., Spiral Solutions Protein Trtmt & Deeply Decadent Cond., CJCCCC reg or lite, KCCC, AO Mandarin Magic, Giovanni LA Hold Hair Spritz + lots more, sporadically
HG Method: Super Soaker-ing + Smasters-ing, short upside down diffusing then clips or clamps & air dry. Blend gray w/henna glosses