Why would you avoid something that looks really great & does feel cooler in hot, sunny temps? You wash your black shorts after every wear. You do the same with white. I have the LG bibs & love them. In answer to some of the concerns:

If you do get something on them, it should wash out just fine. They do not get dingy after repeated washings, they still stay nice & bright. I never use bleach! It is not needed & might ruin the chamois.

They have black in the areas that need coverage, so you do not have to worry about someone seeing more of you than you wish to have exposed. The white areas have some transparency, but this is not in any place where you worry about anything that can be seen. It's not a big deal.

They don't make you look heavy. The cut & the panels are actually very flattering. I love the fit on these bibs, they feel like they mold to your body contours perfectly.

The Assos short also has black panels in the seat area. I do not have it in white, but I do have a pair in red. The fabric is thicker, so my guess is you can't see anything through the white. And that short has a great chamois, too.

I have only had problems with dyes running off saddles on an old pair of red Castelli shorts -- the seating area on those was red, too. I sweated into a saddle that bled black dye onto my shorts. Those shorts have been retired.

For someone who's still afraid of white, the LG should be available in black in the spring. But if you look good in white, go for it!