Need sheet to automatically populate next unique entry entered on a different sheet

I'm looking for a way to have a unique list automatically created and updated as new entries are added to another column.

I have a sheet that has a column of entries, some repeating and some not. I'd like to have another sheet that automatically populates the next new and unique entry when it is entered on the first sheet. Is this possible?

Say Sheet 1 has in column A the following entries:
Red
Blue
Red
Blue
Green
Yellow
Green
Red

Sheet 2 should have the following list:
Red
Blue
Green
Yellow

Then when a new color is added to sheet 1 that's not already on the list, it will appear in the next available cell on Sheet 2.

Thanks.

Nadine

Thanks so much!