Regardless of the way, is it prohibited if I just make it lighter like not making it green or blue or anything?
Say your eyes color is brown.
Dark Brown — Brown — Light Brown
are three different colors as they have different levels of intensity (shades) of the original color (brown).
Here in Wikipedia, they stated:
Brown color names are often not very precise, and some shades, such as beige, can refer to a wide variety of colors, including shades of yellow or red.
They consider the shades of the same color to be different colors.
So, if you were to change the intensity of your eyes color to a lighter one, for example, it would be prohibited (Haram) in Islam as it is considered a different color (light brown) even if it hasn't been standardized by a name yet.
According to the same article:
There are no standardized names for shades of brown; the same shade may have different names on different color lists...
There is a famous hadith:
“What is allowed is that which God has permitted in his book, and what is prohibited is that which God has forbidden in his book, and what he has remained silent about is forgivable.”
Al-Tirmidhi, 1726. Classed as hasan by al-Albaani in Saheeh al-Tirmidhi.
There exist no verses or authentic hadiths which prohibits women from changing their eye colour.
Therefore, It is not prohibited.