When rendering a transparent object in THREE the specular highlight fades along with the diffuse surface of the material. I’d expect it retain the same brightness considering specular is supposed to be more of a mirror like reflection. Here’s a picture of a sphere with the Standard material in THREE:
metalness: 0, roughness: 0.3, opacity: 0.15
And here’s what a similar sphere looks like in Unity, which is more what I’d expect:
metallic: 0, smoothness: 0.8, opacity: 11 / 255
As an aside I’m a bit surprised by the difference in darkness of the transparent objects between THREE and Unity. The THREE material has an opacity of 0.15 while the Unity material has an opacity of 0.043 (11 / 255) and yet they look the same. Switching Unity’s color space from Linear to Gamma makes the results look more similar with the same with the same opacity. Is this a limitation of blending in the current WebGL APIs?