Yellow is a cab that takes you for a ride;
Yellow is a fin a tuna wears with pride.
Yellow is a cake you wouldn't want for tea.
Yellow is 
smiling up at me.
Yellow is a happy face a smile that makes you warmer.
Yellow is the grass's hue come the end of summer.
Yellow is the flag that warns you to take care: Could be danger or infection - you need to be aware.
You can check your answers for this puzzle on Geochecker.com.