Here's how you can answer:
Simple answer:
* "Es [color]." (It's [color])
* Example: "Es roja." (It's red.)
More detailed answer:
* "Es [color] con [pattern]." (It's [color] with [pattern])
* Example: "Es azul con flores." (It's blue with flowers.)
If you don't know or don't want to say:
* "No estoy segura/o." (I'm not sure.)
* "No te lo puedo decir." (I can't tell you.)
Important note: When answering in Spanish, remember to agree the adjective "color" with the gender of "blusa" (which is feminine).