algorithm2e change color of colon (:) after Input/Output

Unfortunately \SetKwInput uses \KwSty internally to set your input/output titles. And, since you've updated \KwSty to include colour, it translates to your \Input.

The solution below implements two items to provide what you're looking for:

• Updates \SetKwInput (with a patch thanks to etoolbox) to use a newly-defined \InputSty rather than \KwSty to set the input-related content. \InputSty now sets its content using \bfseries.

• Setting the content within \InputSty using \eqmakebox[<tag>][l]{<stuff>} (thanks to eqparbox. This sets <stuff> in a box of widest width based on the same <tag> (all left-aligned).

\documentclass{IEEEtran}
\usepackage{amsmath,amssymb,amsfonts}
\usepackage{xcolor}
\usepackage[ruled,lined,linesnumbered]{algorithm2e}

\usepackage{etoolbox,eqparbox}
\patchcmd{\SetKwInput}% <cmd>
  {\KwSty}% <search>
  {\InputSty}% <replace>
  {}{}% <success><failure>
\newcommand{\InputSty}[1]{\eqmakebox[algorithm][l]{\bfseries #1}}

\SetKwInput{Input}{\textcolor{black}{Input}}
\SetKwInput{Output}{\textcolor{black}{Output}}
\renewcommand{\KwSty}[1]{\textnormal{\textcolor{blue}{\bfseries #1}}\unskip}
\newcommand{\Print}[1]{\textit{print}(``#1'')}

\begin{document}

\begin{algorithm}
  \Input{this text}
  \Output{how to write algorithm with \LaTeX2e}
  initialization\;
  \ForEach{\(n \in \mathbb{K}\)}{
    \If{\(n < \tau\)}{
      \Print{Lower}\;
    }
    \Else{
      \Print{Greather equal}\;
    }
  }
  \caption{How to write algorithms}
\end{algorithm}

\end{document}

Compile at least twice on the first go, or with any change in your \SetKwInput content. One can also make this algorithm-specific if needed.

As @Werner explained clearly \SetKwInput uses \KwSty internally to set your input/output titles. And, since you've updated \KwSty to include colour, it translates to your \Input.

This is an alternative solution that doesn't patch \SetKwInput:

• it defines new commands \Input and \Output with \SetKwHangingKw
• since \SetKwHangingKw doesn't print : at end of keyword, [but] line is numbering if linesnumbered is set, we need to patch that behaviour if we want to act like \SetKwInput
• bonus: now you have a new tool at your disposal "\nonl" that let's you disable line numbers for specific lines

Full code

\documentclass{IEEEtran}

\usepackage{amsmath, amssymb, amsfonts}
\usepackage{xcolor}% needed for \normalcolor
\usepackage[ruled, lined, linesnumbered]{algorithm2e}
\usepackage{eqparbox}

% Changing the color of keywords
\renewcommand{\KwSty}[1]{\textcolor{blue}{\textbf{#1}}}

% Aligning Input and Output keywords
\SetKwHangingKw{Input}{\eqmakebox[InOutKeywords][l]{\normalcolor Input:}}
\SetKwHangingKw{Output}{\eqmakebox[InOutKeywords][l]{\normalcolor Output:}}

% Disabling line numbers for specific lines with 'linesnumbered' option on
% code taken from https://tex.stackexchange.com/a/153906/127473, thanks Werner ;)
\let\oldnl\nl% Store \nl in \oldnl
\newcommand{\nonl}{\renewcommand{\nl}{\let\nl\oldnl}}% Remove line number for one line

% Patching 'Input' and 'Output' keywords to prepend '\nonl' command
\NewCommandCopy{\oldInput}{\Input}
\NewCommandCopy{\oldOutput}{\Output}
\RenewDocumentCommand{\Input}{m}{{\nonl\oldInput{#1}}}
\RenewDocumentCommand{\Output}{m}{{\nonl\oldOutput{#1}}}

% Sets up utility commands
\NewDocumentCommand{\Print}{ m }{\text{print(``#1'')}}% 
% you can use it in both text and math mode

\begin{document}

\begin{algorithm}
    \Input{this text}
    \Output{how to write algorithm with \LaTeX2e}
    
    \BlankLine
    initialization\;
    
    \BlankLine
    \ForEach{\(n \in \mathbb{K}\)}{
        \eIf{\(n < \tau\)}{
            \Print{Lower}\;
        }{
            \(\Print{Greather equal}\)\;
        }
    }
    
    \caption{How to write algorithms}
\end{algorithm}

\end{document}