Well, In may daily work I use colors at 255,255,255 for diffuse. It is more obvious for me to see white color as white when setting shaders up. So I usually set up my scene, merge some models, convert materials to Corona, create my materials, and when I finish I just use a script to change diffuse level globally for all materials. In my daily work I use 0,7-0,8 (this is albedo for white plaster - one of the most white diffuse surface I can find). So I consider that white plaster is the whitest diffuse surface in my archtectural scenes so other materials which have bitmaps or colors for diffuse will have a lower values for albedo on exit. This is my way to avoid colors at brightest level and I think this approach is much faster then tweaking each materials.