There was considerable discussion at national committee level on the conspicuity of the new Audax Australia kit. The person driving the design project works also for Orica (yep, same one as TdF team), and consulted with the OH&S boffins there.

It seems that conspicuity is very much background dependent. For example, someone riding with a yellow jersey on roads among fields of in-bloom canola will all but disappear. Try Australian wattle flower for a similar trick. Orange does seem to be a colour that would have trouble blending with anything found on a worksite or along a roadway.

Bright, fluoro colours certainly are effective. Probably the least effective, in my experience, and if I recall from research a long time ago in the auto sector, blues and reds rate among the most difficult.

The issue of conspicuity is one that has been discussed here before. One of the most significant issues that exists, however, is that a cyclist can wear black, blue, orange or any other colour/combinations, but if they are hunched over the handlebars, so the biggest areas (front and back) are hidden from view front and rear, then conspicuity doesn't matter that much.

Next time you are out ona night ride with someone ahead wearing reflective apparel, note how much of its isn't seen, unless there is generous band across the butt area.

As to heat -- I've worn black jerseys from time to time in moderately warm weather. I've not really noticed any difference in heat transfer to my body. The breeze created by riding, and my sweat help moderate that.

I also am someone who wears long sleeves in hot weather to held reduce sunburn on the arms. This is the same at work (in cherry orchards). I have found Coolmax to be pretty good at helping to make me heat tolerable in warm to hot weather.