Just before Pixel fights Acryla, she uses the beam that takes away the ability to change into a Graffiti creature, with the intent of hitting Pixel. When it hits Pastel instead, the curse lasts about ten seconds, not counting the light show that had to happen upon its onset and wearing off. What did she hope to accomplish in those ten seconds that she couldn't have already done while Pixel was in human form? And it's not like the curse only lasted that long because it just grazed Pastel or something; Acryla made sure to absolutely fry her, even after it clearly wasn't going to hit Pixel. Moreover, what did Palette hope to accomplish by using the same beam after her battle as she was fading away? It would have lasted ten seconds, and she was on her last legs anyway. Alright, I'm done.
Given how Tablet appears hurt after being hit by Palette, who says "you may never recover from a blast that strong," it seems that Palette's beam wasn't the same as Acryla's. Acryla's removed one's ability to become a graffiti creature, while Palette's would simply harm whoever's hit. She probably just wanted to get one last (hard) hit in on Pixel to get back at him for defeating her. As for Acryla, she could probably clobber a defenceless Pixel during those ten seconds that he would have been human. If what happened to Pastel is any indication, he would have been paralyzed and just sitting there to be taken out in one good hit.