How do you write genotypic and phenotypic ratios?
I don't think there is formal notation for those ratios.

One would note that perfect dominance and recessivity, perfectly discrete phenotypes without pleiotropy and without environmental variance is extremely rare and these examples are pretty much only encountered in intro classes but never in the real life. There is hence, for the phenotypes at least, really no need for any formal notation here.

That being said, out of clarity, I would definitely prefer 0:0:4 (genotypes) and 0:4 (phenotypes) over 4 (for either genotype or phenotype) and I would definitely prefer 2:2:0 over 2:2