Transparent part of my image shows up black I would like to ask for help figuring this one out.

I have a grayscale image with a black background, and I have the same image but colorized and with transparent background.

I need a mixed shader so that the black is gradually transformed into transparent, while the grayscale is transformed to a color scale.

I tried with a ColorRamp but the alpha becomes black in the render even if I have a blend mode to "alpha blend".

It would be nice if I could symply use the grayscale image texture for it, but I could also use on where I load the two images and mix them.

Thanks for any help

Edit: I add the real RGBa if you want to try it with this images
Works just fine with the provided images.
Perhaps you forgot to connect the alpha channel?