it will be deep red colour if added to acidic solutions.
When salt is added to lemon juice, the sodium ions react with a compound called anthocyanin present in some lemon varieties, resulting in a color change to blue. This reaction alters the structure of the anthocyanin molecules, causing them to reflect light differently and appear blue in the presence of salt.
lemon juice
When lemon juice, which is acidic due to its citric acid content, is mixed with bromothymol blue, the indicator changes color. In acidic conditions, bromothymol blue turns yellow. This color change indicates the presence of acidity in the lemon juice, demonstrating how pH indicators can reveal the acidity or alkalinity of a solution.
what is the initial and final colour of the lemon juice
water
Adding China rose (hibiscus) to lemon juice will result in a refreshing and tangy drink that combines the floral and citrus flavors. The China rose might impart a deep red color to the lemon juice, enhancing its visual appeal as well.
When you mix lemon juice with bromothymol blue (BTB) solution, the color will change from blue to yellow. This is because the acidity of the lemon juice causes the BTB indicator to shift to its yellow color.
if its pure lemon juice with no added sugar then it has no sugar in it. and most lemon juice are like that. its in lemon soft drinks and lemon cordials that add the sugars.
the colour of lemons
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.)
It is called denaturation
When lemon juice is mixed with vinegar, it does not change color significantly. Lemon juice is already acidic and adding vinegar, which is also acidic, will not produce a significant color change.