Multiple materials or texture

My artist sent me a 3D object that used multiple materials to color the model in solid colors, rather than using a texture. However I notice in Unity the model seems very high on the vertex count. If I recall correctly, I believe Unity is multiplying the vertex count for each material attached to the model?

So I wondered if it might be better to use a simple texture instead of the multiple materials — is there a general belief with Unity mobile development which approach is better?