Full Idea
Berkeley seems to have confused the colour of the thing apprehended with the act of apprehension; probably either of these would have been called an 'idea' be Berkeley.
Gist of Idea
Berkeley probably used 'idea' to mean both the act of apprehension and the thing apprehended
Source
comment on George Berkeley (Three Dialogues of Hylas and Philonous [1713]) by Bertrand Russell - Problems of Philosophy
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.22
A Reaction
If we are saying that Berkeley's error was entirely verbal, there is a chicken-and-egg problem. He was an idealist, so he wouldn't have thought that there were two separate concepts behind the word 'idea'. Russell merely asserts that there are.