yellow and black

i was on my way home from NTU this evening
and what i had seen on the train
around 730pm
the train was quite crowded cos it's weekend
and families were out to town
at tht hr everyone was going home as well; just like me
due to the crowd the surrounding was damn noise
fat young couples kissing and touching
and
kids were yelling and running around
(can u imagine how they can do tht in the train)

suddenly, there was this "something" attract my attention
and my mind just had this tot
this object
made me think:
" what is the difference between
YELLOW color and BLACK color?"