Use ADDITIVE_BLEND to achieve emissive effect

I want to achieve an emissive effect (the tail flame effect shown in the figure below).I use the ADDITIVE_BLEND parameter to set the rendering state, but there is no effect. In my opinion, when using the ADDITIVE_BLEND parameter, the color should become brighter and closer to saturation due to the accumulation of colors. But the test code shows that it seems to be no difference from other blending parameters, why? Is this a bug in cesium? How should the emissive effect be achieved?

Here is my test code.

The following is the running result.