yellow
They both create mixtures called solutions.
lemon juice
Lemon juice!
The litmus papers are used for checking the acidic and basic nature of any substance. That's why drop of lemon juice, which is by nature acidic, turns blue litmus into red(as the property of acidic solution is to change the color of blue litmus to red). So soap solution which is by nature basic will turn red litmus into blue (as the property of basic solution is to change the color of red litmus to blue).
It's possible that the asparagus juice contains an indicator chemical which is reacting to the acid in the lemon juice. (Note that I don't know exactly which indicator is involved, or even if this actually happens; I'm just offering an explanation for the phenomenon you say you've observed.)
Red in acidic solution
The color remain red because vinegar is an acidic solution.
add lemon juice
No, lemon juice is acidic, it's citric acid.
EXPLOSION!
lemon juice
no
what is the initial and final colour of the lemon juice
They both create mixtures called solutions.
You shouldn't
No. Lemon juice is acidic, so it will have a lower pH.
the colour of lemons