Thran Lens or other color-changing effects have no effect on Devotion.
700.5. A player’s devotion to [color] is equal to the number of mana symbols of that color among the mana costs of permanents that player controls.
The mana symbols in a card's mana cost determine the card's color, but not the other way around.
105.3. Effects may change an object’s color or give a color to a colorless object. If an effect gives an object a new color, the new color replaces all previous colors the object had (unless the effect said the object became that color “in addition” to its other colors). Effects may also make a colored object become colorless.
The above rule covers everything about changing an object's color. Note that it does not say anything about mana symbols being changed, so nothing like that happens.