Setting color mode to HDR in a shader node makes virtually no difference. It always appears as a "flat", default color. I am using Unity 2019.1.13f1, the problem only appears in LWRP. The same shader in HDRP works as intended (see below).
The HDRP example has post processing with Bloom enabled. The LWRP example does not. The default sample scene for both render pipelines should have post processing and bloom enabled by default, which makes me think you disabled it in the LWRP scene on accident.