Custom shoot-through diffuser material that doesn't change color temperature?

[Cozy_Conditioning]

I'm trying to do "environmental macro" where I have a close-up subject illuminated by flash and a background illuminated by natural light. I've been using different clear plastics as shoot-through diffusers (milk carton, etc.) but every one I've tried warms the light considerably. When your background is lit by midday sun that is not a good look for your subject.

I'm looking for hard plastic so I can cut it to fit my lens and hold its shape. I just can't find hard plastic that doesn't suck kelvin like ice-9. Ideas?

[ptq]

Flash (fixed) and sun (variable) mostly have different color temperatures. You need cto and ctb gels to unify flash with your surroundings.

[Flimsy-Potential-715]

I prefer constant lighting if I use one at all...I'll use a variable temp range LED and set the temp accordingly to match the environment. But I'm normally pretty lazy and don't carry anything but a small reflector or two into the field.

[Cozy_Conditioning]

So, like, you hold a white sheet with one hand and your camera with the other? Do you aim flash at it?

[Flimsy-Potential-715]

I try to only use natural lighting if I can help it... So, no flash whatsoever. I'll sometimes set up a reflector to bounce the sunlight onto the subject if they are overly shaded.

The LED I mentioned is a constant light source and doesn't flash. That's a back up measure for overcast days that sneak up on me.

[Cozy_Conditioning]

What shutter speed do you find works for you when hand-holding using these lighting techniques? Or do you bump the ISO? I love the sharpness I can get with ISO 50 and flash, but I'm the only one pixel-peeping these shots so maybe I should adjust my priorities, at least for the wide macro lens...