One today equals two tomorrows means that what you can accomplish today is more important than what you have planned tomorrow. Today is now. Do something today if you are able to do it. Tomorrow is not guaranteed. The time that you have in life is limited. You have to accomplish one day at a time without thinking about a tomorrow.
I agree with that because if you don't do what you planned to do today, you will probably never get another day to do it. Life can be very unpredictable and I think you should take one day at a time and live your life to the fullest.
In this sentence Yellow and black would be the compound subject. Yellow and black are both subjects and the use of the word 'and' lets you know it is a compound subject.
