What could be the reason for converting a rgb-black on a png-image into grey when the image is embedded in an HTML-Code?

today I wanted to embed an png-image into an HTML-site. I painted the Image with Adobe Illustrator and the Color of my painting is RGB-black(0,0,0). Exported, it appearanced also okay. But as I embedded it in my HTML-Code and viewed my document in the Browser ( MS Edge), the color sometimes didn't appearanced black anymore, it was a lighgrey. In the previewmode of Adobe Dreamweaver i've the same Output.

What can I do , that the Output looks the same as the normal Image? Thanks a lot. The difference between the two Frames can be seen clearly