can you use enamel paint reducer to effect paints translucenecy?

[Nick D]

we're doing a paint project in school using primary color enamel we have to mix to our custom colors, the paints intended for tractors and such we're mixing it 4:1 with a medium reducer can i use a different ratio to effect the translucency of the paint such as spraying a semi translucent goldish color over a light gray stripe to acheive a semi metallic gold finish