You must learn a special skill to tame Lesser Dragonkin. For pets of this family other than cloud serpents, the skill is taught by the tome, How to Train a Dragonkin. This is awarded by Kaestrasz in Valdrakken at renown level 23 with the Valdrakken Accord. It is only awarded to hunter characters with the appropriate renown, you cannot achieve the renown on a non-hunter alt.
This fey darter can spawn during Superbloom events, but only when the Fae Lens ability is on offer from the dreamfruit. This only happens when the Superbloom takes the western/counterclockwise path around Amirdrassil. You may have trouble taming one of these darters before someone kills it, but it's also not a unique colour.
Found in a number of areas, including Amirdrassil, Viridescent Thicket, Shoreline Roots, Fields of Reverie,Whorlwing Basin, Sprigling Gloam, and Skystone Falls. Also found in the glades north and east of Amirdrassil, as well as west of Haven Cascades.
Level scaling: Most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.