More on rendering alpha blended sprites

Hello,
I am trying to make some headway in terms of rendering alpha blended sprites. I am using OSLib, and I’m on RISC OS 5.21 (8th April 2014). Here is what I have so far:

if I open up the screenshot sprite in PrivateEye, I see this:

So it would appear to me that I do in fact have an alpha blended sprite, but cannot display it correctly.

I’ve been advised to change the mode word, and my attempt to do that, is such:

osspriteop_header * header = wimpspriteop_select_sprite("sunset");<br/> header->mode = (os_mode) 0x78608051;<br/> wimpspriteop_put_sprite_user_coords("sunset",x,y,os_ACTION_USE_ECF4);<br/>

So, am I not changing the mode word correctly, or is my rendering wrong?

Looking at the sprite in PrivateEye makes it appear like somewhere along the way, my rendered sprite is considered alpha-blended, it just does not look like it is!

Any help, very much appreciated.

Thanks

Garry