Actually, both words are acceptable.
I'm old enough to know that "bold-faced" is recent usage. Here's information cribbed from a couple of sources:
The original term seems to have been bald-faced (bare-faced) and refers to a face without whiskers. Beards were commonly worn by businessmen in the 18th and 19th century as an attempt to mask facial expressions when making business deals. Thus a bald-faced liar was not a very good liar, and was not able to lie without the guilt showing on his face.
It's just the last 5 years or so that "bold" has come into usage. It refers to a typeface. It is used metaphorically in speech. In the same way that a typesetter uses bold face type to highlight specific text and set it apart, a bold face lie stands out in such a way as to not be mistaken for the truth.
...and yet people wonder why our nation is so 'dumbed down'.
Never mind that 'dumbed' is also modern slang and not proper English.
Ask yourself this... what does 'bald faced' even mean ? What relevance does the term 'bald faced' have to the word 'liar' ?
My guess is that the term 'bald faced' came about through ignorance, but was in enough use that it got put into the lexicon as 'acceptable'.
Just like "ain't".