Testing to see if this would work with 1.16.4, I get this error -

[19:10:22] [main/FATAL]: Mixin prepare failed preparing compat.IdentifierMixin in colormatic.mixins.json: org.spongepowered.asm.mixin.transformer.throwables.MixinTargetAlreadyLoadedException Critical problem: colormatic.mixins.json:compat.IdentifierMixin target net.minecraft.class_2960 was loaded too early.
org.spongepowered.asm.mixin.transformer.throwables.MixinTargetAlreadyLoadedException: Critical problem: colormatic.mixins.json:compat.IdentifierMixin target net.minecraft.class_2960 was loaded too early.
at org.spongepowered.asm.mixin.transformer.MixinInfo.readDeclaredTargets(MixinInfo.java:938) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinInfo.(MixinInfo.java:872) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinConfig.prepareMixins(MixinConfig.java:715) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinConfig.prepare(MixinConfig.java:652) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.prepareConfigs(MixinProcessor.java:514) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.select(MixinProcessor.java:439) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.checkSelect(MixinProcessor.java:415) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:285) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:208) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:178) ~[sponge-mixin-0.8.2+build.24.jar:0.8.2+build.24+unknown-b24.git-unknown]
at org.spongepowered.asm.mixin.transformer.FabricMixinTransformerProxy.transformClassBytes(FabricMixinTransformerProxy.java:23) ~[fabric-loader-0.10.6+build.214.jar:0.8.2+build.24+unknown-b24.git-unknown]
at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:157) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:150) ~[fabric-loader-0.10.6+build.214.jar:?]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_271]
at java.lang.Class.forName0(Native Method) ~[?:1.8.0_271]
at java.lang.Class.forName(Unknown Source) ~[?:1.8.0_271]
at net.fabricmc.loader.util.DefaultLanguageAdapter.create(DefaultLanguageAdapter.java:45) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.EntrypointStorage$NewEntry.create(EntrypointStorage.java:114) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.EntrypointStorage$NewEntry.getOrCreate(EntrypointStorage.java:101) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.EntrypointStorage.getEntrypointContainers(EntrypointStorage.java:186) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.FabricLoader.getEntrypointContainers(FabricLoader.java:272) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:44) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:36) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:139) ~[fabric-loader-0.10.6+build.214.jar:?]
at net.fabricmc.loader.launch.knot.KnotClient.main(KnotClient.java:27) ~[fabric-loader-0.10.6+build.214.jar:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_271]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_271]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_271]
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_271]
at link.infra.jumploader.Jumploader.onLoad(Jumploader.java:171) ~[?:?]
at cpw.mods.modlauncher.TransformationServiceDecorator.onLoad(TransformationServiceDecorator.java:53) ~[?:?]
at cpw.mods.modlauncher.TransformationServicesHandler.lambda$loadTransformationServices$11(TransformationServicesHandler.java:131) ~[?:?]
at java.util.HashMap$Values.forEach(Unknown Source) [?:1.8.0_271]
at cpw.mods.modlauncher.TransformationServicesHandler.loadTransformationServices(TransformationServicesHandler.java:131) [modlauncher-8.0.6.jar:?]
at cpw.mods.modlauncher.TransformationServicesHandler.initializeTransformationServices(TransformationServicesHandler.java:56) [modlauncher-8.0.6.jar:?]
at cpw.mods.modlauncher.Launcher.run(Launcher.java:76) [modlauncher-8.0.6.jar:?]
at cpw.mods.modlauncher.Launcher.main(Launcher.java:66) [modlauncher-8.0.6.jar:?]

RER also gave me a very similar error upon updating to 1.16.4. 1.16.3 works fine though. Lemme know if you need any additional information.

MC 1.16.4
Fabric 0.6.1.51
Colormatic 2.2.7

What is your full mod list?