OK I see.
The problem is coming from old Helix version, where titles colors was not available.
and now, with new helix version, titles color cutomisation is available.
And by default, with new helix version, titles color value is black instead of being empty.
This is problem because titles are not necessary black and now this needs to be corrected manually.
Is it possible to improve that point on new helix version ?
For instance, set by default titles colors (h1,h2,h3 etc..) to empty (nothing) instead of black.