Caramel sauce can get it's color/flavor through two separate and unique processes. Some recipes use one, some the other, some both.
1. Browning cream/butter
2. Browning sugar
Because of the proteins in cream, a cream/butter based caramel sauce will begin to color at very low temps, especially with prolonged cooking- temps as low as 200. The milk solids in butter perform the same way, to a slightly lesser extent. The nutty/toasty notes of browned cream/butter make for a fairly mild tasting/lightly colored caramel, assuming of course the caramel isn't brought too much above 300 deg for any duration of time. If you expose a cream based caramel to temps above 300 degrees for too long- the cream will eventually brown too much and go bitter. A kraft caramel is a good example of the type of caramel (light color/mild flavor) that lightly browned cream produces.
Cream browns in the 200-300 degree range. Sugar, on the other hand, doesn't begin to color until 305, so you can see how were talking about two different processes here:
Cream = low temperature browning
Sugar = high temperature browning
A lightly colored/mildly flavored browned sugar sauce is in the realm of possibility, but, generally speaking, browned sugar caramel sauce is usually darker/more flavorful than it's browned cream cousin. Getting the right color when browning sugar not only takes some practice, but it involves some understanding of the complex flavors being created and how society perceives them. Caramel, coffee beans and roux all share similar turf when it comes to public perception. Although you have some people that grew up with very darkly roasted coffee beans or very dark roux, most people aren't accustomed to them and prefer slightly lighter versions. A penchant for darkly roasted, bitter (more alkali) flavors isn't something people are born with, it's acquired. Darkly browned sugar caramels are the same way. I'm not saying that dark caramel sauce is bad, but if you're not accustomed to it, you might find it bitter. Also, much like darkly roasted coffee beans and very dark roux, the window between dark and burnt caramel sauce is minuscule. As you cook it, it will be a lovely shade of reddish brown and a split second later, it's black. Another important factor in this equation is that sugar will continue to cook after to you take it off the heat (unless you add liquid) so whatever shade you remove it at, it will end up slightly darker.
When browning sugar for caramel sauce, I think it's a good idea to err on the side of caution and under brown it, at least until you both master the practice and ascertain how dark you prefer it.
I, personally, am not a big fan of darkly roasted flavors, but a browned cream caramel isn't flavorful enough for me and a browned sugar caramel, when browned enough to become flavorful, tends to be bitter. For this reason, I utilize the best of both words by utilizing a 2 stage process to brown both the sugar and the cream. I lightly brown my sugar at the high temp, add cream, lightly brown that at a lower temp, then add water to achieve the consistency I want. I find this gives me a very rich bold flavor without any bitter notes from over browning either ingredient.
One last thing to consider when browning sugar is the dessert it's being used in. Although for a caramel sauce for ice cream, I'd go very light with my sugar, for a flan (where the layer of sugar is fairly thin), I might go a few shades darker.