Both mutations are not dominant. Greywing is recessive. Opaline is sex-linked.
To produce a greywing chick visually, mom must give 1 greywing gene and dad gives the other greywing gene. Both mom and dad can be split for greywing and therefore not seen visually.
To produce opaline chick, dad can be split or visually opaline to produce female opalines. Female opalines can only be seen visual to have opaline gene and she cannot be split for opaline. This is sex-linked mutation. Opaline male chicks must have 2 opaline genes, one each from mom and dad.
As Roland has said neither is dominant. Most mutations do not have an order of dominance. They can appear either separately or together. When you are calculating the inheritance of mutations work each one out according to it's own rules, then combine the results