Where did you hear these myths? How much did you look into these myths before arriving here?
A ripe lemon is usually a clean, pale-yellow color.
Surprisingly, a ripe lime is actually more yellow than green! But, a lime is usually best used in recipes when still green. In regard to limes, this is what the World's Healthiest Foods website has to say:
"They should have a glossy skin that is deep green in color; although limes turn more yellow as they ripen, they are at the height of their lively, tart flavor when they are green in color."
Red sweet peppers have about twice as much sugar as green "sweet" peppers. The green peppers are unripe and usually bitter. They will become red as they ripen and they will sweeten up accordingly.