A recessive gene effects phenotype - it has no change in the allele frequency of the population.
Evolution is a change in the DNA of a population.
Hiding the recessive gene for blue eyes behind a gene for brown eyes is mixing and matching those alleles - it changes nothing as far as their prevalence within the population.
Your understanding of the very basics of biology is completely lacking.
No. If an environmental change made blue eyes disadvantageous to survival and reproduction, that population would gradually “evolve” to possess DNA for brown eyes only.