placing image changes colors RGB -> CMYK

Hi fellow designers,

I'm creating a document in InDesign working in RGB mode since it's purpose is only web-view pdf.
It consists of both text and images. On one of the pages I have to insert a certain amount of logo's from several companies.

However, one of those logo's (a .png created in Photoshop, using greyscale workspace) causes the colors I use in the document for e.g. text, to change from bright RGB colors to flat CMYK-like colors.

At first I thought it was only an indesign preview thing, which would be solved by creating an RGB PDF. But unfortunately the color stays flat even in pdf. I've tried all sorts of ways to both save the images and export the pdf but the problem continues.

Does anybody have to answer to solve this problem?

Thanks.