First, we load some colorbar data and define val for testing

Get["https://pastebin.com/raw/gN4wGqxe"] vals = N@Subdivide[200000]; 

then, definition

ClearAll[ParulaCM, ParulaCM2]; ParulaCM =    With[{colorlist = RGBColor @@@ parulaColors}, Blend[colorlist, #] &]; ParulaCM2 =    With[{colorlist = RGBColor @@@ parulaColors},     Blend[colorlist, #] &]; 

You may notice that ParulaCM and ParulaCM2 is exactly the same. I do it on purpose.

Now timing it

ParulaCM /@ vals; // AbsoluteTiming ParulaCM2 /@ vals; // AbsoluteTiming 

with a fresh start you may probably got this

{0.400419, Null} {1.03218, Null} 

This is already odd, because ParulaCM is the same as ParulaCM2. However, ParulaCM2 is slower

Now you run the previous definition a second time, and time it again. This time you probably got

ParulaCM /@ vals; // AbsoluteTiming ParulaCM2 /@ vals; // AbsoluteTiming (*{1.12729, Null} {1.07233, Null}*) 

Yeah, they are same again!!

Now even more peculiar, now you run this

Wow, the ParulaCM is fast again.

I am totally lost. What kind of issue is this?