Critical hit presentation

I'm trying to setup weapon damage with D&D rules.
e.g. Dagger damage is 1d4, critical hit is 19-20, multiplier is 2

I've setup a formula below and works fine.
((Math.randomInt(20)+1)>=19)?(Math.randomInt(4)+1)*2: (Math.randomInt(4)+1)

But the problem is in playtest, I can't distinguish between normal attack and critical hit.
Is there any way to change the damage color to RED or display a message when critical hit is made?

wouldnt it be easier to just make those attacks just have a 10% crit chance and use a plugin to change the crit modifier to x2 instead of the default x3
http://yanfly.moe/2015/11/07/yep-25-damage-core/
is required to use
http://yanfly.moe/2015/11/08/yep-26-critical-control/
which will allow you to change the crit modifier.

Thx for your advice! It works great.

I am using YanFly Weapon unleash, Damage core & Critical control plugins
My existing setting is:
<Weapons>
0001: Dagger
Note: <Replace Attack: 1>
<Certain Hit Critical Rate: +10%>
<Critical Multiplier: +200%>

<Skills>
0001: Dagger
Formula: Math.randomInt(4)+1
Note: <Critical Rate: 0%>
<Critical Multiplier: 0%>

Under my logic, I have to setup more Skills for different damage roll.
Seems not very precise.
Is it possible to add damage formula under Weapons tab?

Just answer to my own question.
I found this thread which is exactly what I want.
https://forums.rpgmakerweb.com/index.php?threads/weapon-damage.56370/

Does YanFly's plugin also have this similar function?
As I'm new in RPG maker, want to focus on single series plugin first.