You can edit the style of any gradient inside the Gradient Editor menu
After choosing a preset gradient, more swatches can be added to the array of colours along a gradient’s preview by clicking anywhere underneath.
It doesn’t matter which colours are chosen, but darker ones create a stronger contrast when the gradient is given the Screen blend mode.
Try out other presets, such as the Noise Samples. This increases the number of transitions in the gradient, which work great for beams of light, if that’s what you’re going for.