Could someone please explain 'ticking', thank you?.

Hairs, of a different colour, sprinkled throughout a coat.

http://www.doggenetics.co.uk/ticking.html

is it always on a white coated area?

In dogs it does seem to be - but not in other species.

Thank you, in hounds is there a difference between heavy ticking & spots?

> Thank you, in hounds is there a difference between heavy ticking & spots?

I'm really not sure - maybe this link will help? It's gundogs rather than hounds, though.
http://homepage.usask.ca/~schmutz/dogspots.html#ticking

Spots are generally bigger than ticking/flecking. In dalmatians spots appear several weeks sooner than flecks.

Seems to depend on species.  With cavies there is a Golden Agouti.  It's a "ticked" animal.  The dark golden hair has black at the end of the hair shaft.  So two different colours on the same hair.