Will one pair fit me through the whole pregnancy?

Yes, and this is specifically why the adjustable button waistband exists. As the bump grows you extend the waist mechanically rather than relying on the fabric stretching further and further. Most women wear the same size from the second month through to full term.

Why is the gusset white?

It is a deliberate design choice. During pregnancy, discharge changes in colour, consistency and volume are things midwives ask you to monitor. A white cotton gusset makes that straightforward rather than something you have to think about.

Does the panel feel too warm in the later months?

The ribbed cotton breathes well, so the double-layer panel adds coverage without trapping heat. It sits comfortably through the day without building warmth the way synthetic fabrics do.