Color specific sections of a texture

Hello, everyone.

I have this code, which allows the user to choose the colors of certain sections of the character's clothes. It works by taking a base color-coded texture and replacing the colors in it for the ones the player chooses, but I have a problem.

     public void Gen()
     {
         ShirtColor = MyPicker.corShirt;
         ShortsColor = MyPicker.corShort;
         SocksColor = MyPicker.corSocks;
         DetailColor = MyPicker.corDetail;
 
         int contx = 0;
         int conty = 0;
         foreach (Color32 pixel in tex1.GetPixels())
         {
             if (pixel.r < 120 && pixel.g > 100 && pixel.g < 250 && pixel.b > 230)
             {
                 Finaltex.SetPixel(contx, conty, ShirtColor);
             }
             if (pixel.r < 120 && pixel.g > 140 && pixel.b < 10)
             {
                 Finaltex.SetPixel(contx, conty, ShortsColor);
             }
             if (pixel.r < 115 && pixel.g < 115 && pixel.b > 140)
             {
                 Finaltex.SetPixel(contx, conty, SocksColor);
             }
             if (pixel.r > 130 && pixel.g < 90 && pixel.b < 90)
             {
                 Finaltex.SetPixel(contx, conty, DetailColor);
             }
             if (contx < tex1.width - 1)
             {
                 contx++;
             }
             else
             {
                 conty++;
                 contx = 0;
             }
         }
         Rp = MyPicker.R;
         Gp = MyPicker.G;
         Bp = MyPicker.B;
         Finaltex.Apply();
         gl.generated = Finaltex;
         
 
     }

It works, but it's too slow. I only call it once, when the player confirms the color they want, but still, the delay is too uncomfortable in smartphones.

Is there a better way to do this? Can a shader be used for that?(I understand nothing of shaders...) Or maybe a more efficient algorithm instead of checking each pixel?