1. A blonde person has dyed their hair and their roots have grown out
2. A phrase used to tell someone who doesn't have blonde hair that they are stupid or ditzy because of the stereotypical idea that blonde people are stupid or ditzy
Tanya: "OMG, did you know that Niagra Falls is in Canada?"
Rebecca: "Um duh, everyone knows that"
Tanya: "I just foud out! Isn't that awsome?"
Rebecca: "Careful Tanya, your blonde roots are showing"
Tanya: "Wha? Im not blonde!"