What colors of sea glass are considered rare? 

Red sea glass , orange sea glass (the least common type of sea glass, found once in 10,000 pieces), purple sea glass, cobalt and cornflower blue (from early Milk of Magnesia bottles, poison bottles, artwork, and Bromo-Seltzer and Vicks VapoRub containers), and aqua (from Ball Mason jars and 19th century glass bottles.) Hope this helps!

Rare colours vary from country to country too, though red and orange are rare everywhere, we find very little amber compaired to the USA here in the UK, and we have things that are pretty unique to our beaches, the english multi, many colours in a single piece, these are very rare, worldwide. Our sand level has risen by about 6 foot in the last 18 months or so, so our glass is much rareer than it used to be, we don't mind though, being found more gently will ensure it lasts for many more years.

I hope you do!! You have to be actually looking for it I find, then you have more chance of spotting it, not sure why, but if I am looking for a particular colour, or shape of sea glass I often get lucky, compaired to finding something out of the blue. Good luck!! x