the black color is a must?

Not necessarily......

please feedback.

Hello Sir,
First of all thank you so much for inviting us in your project and really apologize for not submitting our submission on time as we were busy in another project, but we had worked on some 5 versions of the logo designs considering the deadline 20 hrs today in the morning. But unfortunately you have chosen the winner before deadline we guess. But we want to show our concepts. So is there any possibilities?

Awaits for your feedback.
Thanks