When analyzing dna microarray results, why are colors turned into ratios?

Idon’t know the answer and i’ve been stuck on it for a while now skskskskks

Aresearcher created three groups based on participants bmi: normal weight, overweight and obese. the hypothesis being tested is that the three groups differ in the mean number of artificially sweetened drinks consumed weekly. which statistical test might the researcher use, assuming a reasonably normal distribution of values.

Which level of taxonomy has the fewest organisms?