Earlier quoted context omitted.
They edited embryos: we determined whether a TDO-selective inhibitor (680C91) impeded pigmentation in developing embryos. The development of D. pealeii has been divided into 30 stages and eye pigmentation appears at ∼stage 25, while chromatophore pigmentation starts at stage 26 [21]. We added 680C91 to developing embryos at stage 20
While you're right they edited the embryos the sentence you quoted is describing a drug (680C91) that they bath-applied to inhibit the TDO enzyme (as a positive control), rather than the CRISPR strategy they used, in which they injected the Cas9 and sgRNA into the embryo.
Knocking out TDO in squid embryos efficiently eliminated pigmentation. By precisely timing CRISPR-Cas9 delivery during early development, the degree of pigmentation could be finely controlled.