A lot of people have differing opinions on this, but let's face it, for a woman, it's a fact of life having to wear bras. And if you like tank tops, why should you feel insecure about whether or not your bra strap shows? Like you, braless isn't an option for me, but I tend to wear at least two tank tops (one thicker strapped, and one "spaghetti" strapped) over a black strapped bra, and nobody's made a comment about it. Even with the dress code of my job (no tank tops with straps less than 2 inches), because my "spaghetti" strapped tank tops are generally black, and most of my bras are black strapped anyway, nobody's noticed, and if they have, they haven't said anything.
As for clear bra straps, I've never tried them, but I can only imagine that plastic is going to get uncomfortable in the heat and sun.
Hope this helps.