Found this guy at a site near Haad Chao Lao, Chantaburi Province, Thailand - depth 4m. I think it's some kind of Pseudoceros sp. - ID help please...
Apologies for poor quality of photo. The small single spot on the flatworm's head is not a grain of sand but is an actual colouration.

Sorry, don't see a picture. Could be my computer though?
Sorry, don't see a picture.
Here it is as an attachment.

Hi Vie - Welcome to Wetpixel. 
I couldn't find an exact match for your animal. Take a look at Pseudoceros indicus http://pick5.pick.uga.edu/mp/20p?res=640&see=I_ML277 - could yours be a light colored variant of this species?
Hi Vie - Welcome to Wetpixel.

Thanks, Leslie. Nice to see a familiar avatar here 
I couldn't find an exact match for your animal. Take a look at Pseudoceros indicus - could yours be a light colored variant of this species?
Could be! The Pseudoceros indicus photos below show violet/purple margins - I have never seen the variant that you linked (above) before. Thank you.
http://www.rzuser.uni-heidelberg.de/~bu6/flat0369.html
http://www.rzuser.uni-heidelberg.de/~bu6/flat0389.html
Could be! The Pseudoceros indicus photos below show violet/purple margins - I have never seen the variant that you linked (above) before. Thank you.
Leslie Newman identified all 3 images and she described the species so I guess they're probably right

the original description says either blue or purple spots. It's here: http://mangilao.uog.edu/up/micronesica/abs...man_177-184.pdf
And here's another color variant
http://www.nudibranch.com.au/pages/6646a.htm
Excellent. Thank you for all the info 