]
2 CrO42-(aq) + H2O(l)	↔	Cr2O72-(aq) + 2 OH- (aq)
chromate		dichromate

Adding acid decreases the [OH^-] through neutralization. Solution turns orange.

2 CrO₄^2-(aq) + H₂O(l) → Cr₂O₇^2-(aq) + 2 OH^- (aq)↓

Le Châtelier causes shift → to restore some of the OH^- (aq) as this happens the dichromate (orange) concentration increases too.

Adding base increases the [OH^-] . Solution turns yellow.

2 CrO₄^2-(aq) + H₂O(l) ← Cr₂O₇^2-(aq) + 2 OH^- (aq)↑

Le Châtelier will shift ← to decrease [OH^-] as this happens the chromate (yellow) concentration increases.

Note:

Adding water as no significant change since its concentration (56 M) so the water concentration will not significantly change significantly.