There actually is! :D
Well tha means 'is' so grammatically it could mean 'A pink house is in Portree'. That would really mean the same thing as 'there is...' but would not be good English. It is simply that you need the word there to express the existence of a pink house in English but you don't need anything in Gaelic, and this is the specific point they are trying to teach here – how to translate there is.
Note that without the 'in Portree', you would have to add the adverb ann:
Tha taigh pinc ann 'there is a pink house', 'a pink house exists'
Note also that the English word there is ambiguous. Here it is being used to express existence. It can also be used to say where something is:
Tha taigh pinc an-sin 'there's a pink house', you say, pointing at it, as you had been looking for coloured houses. This can actually happen if you are driving round Portree – you can see several coloured houses in surprising places and need to point them out.