How do colored spectral emission lines relate to frequency?
As you can see these emission lines come in all sorts of colors, which are characteristic of the photons emitted when an electron goes back to its ground state in certain atoms (e.g. H, Na, et cetera).
If we look above, we notice that hydrogen's spectrum has a red line and some "bluer" lines to the right. These are higher energy photons due to the color, usually n = 5 or 6 to n = 1 transitions.
If you remember...
Frequency is directly proportional to energy! Now, tell me, are high energy lines high or low frequency?