Making Pure black on the gray scale colour

[Charmaine Fritz]

I have an image that is pure black on the gray scale and when I try and use the colour fill it makes it not the colour I close - yellow, but another grey colour.
What do I need to do to over come this. Currently using CS6

i'm fairly new to PS so guidance on menu selection would be appreciated.
Thank you

 

[MrToM]

Try this:

IMAGE > MODE > RGB Color

Regards.
MrToM.