Quo Vadis offers 16 fountain pen friendly planners with 90gr paper. See most of them here.
The weekly formats include 9 calendar year (Dec.-Dec. or Jan.-Dec.) and 4 academic year (July-July or Aug.-July).
All the monthly formats – Visoplan (12 mos.), Exaplan (21 mos.) and Monthly 4 (18 mos.) – are fountain pen friendly.
Most have white paper; but Visual and Space 24 have Registre Azur paper (a very light green), and Note 27 features ivory paper.
My planner is a Sapa X (64 g). I often use pencil, but sometimes I’m in the mood to write with a pen. Since I use a fine point nib and fast-drying ink I rarely get bleed-thru. My preference is white paper with a fountain pen. Perhaps it is my imagination, but I experience the ink colors more vividly with white paper vs. ivory or the green.
Do you write in your planner with a fountain pen? If so, what is your experience, and does the color of the paper make a difference to you?