how to find specific values in a column

I have this dataframe:

    yellow_col green_col  red_col blue_col 
    
    yellow      none       none    none
    
    none        green      none    none
    
    none        none       red     none

I want to find and place the values in a new column like this:

 

    yellow_col green_col  red_col blue_col  color
    
    yellow      none       none    none     yellow
    
    none        green      none    none     green
    
    none        none       red     none     red

I tried many ways and this is the last

    for i in range(len(df_arch_copy)):
        x=df_arch_copy.query('red_col=="red"or green_col=="green"or blue_col=="blue"or yellow_col=="yellow"').index
        df_arch_copy.color.insert(x,inplace=True)

Answer

Try this:

import pandas as pd
colors=[]
for row in df.values:
  for color in row:
    if color!='none':
      colors.append(color)
df['color']=colors
print(df)     
  yellow_col green_col red_col blue_col   color
0     yellow      none    none     none  yellow
1       none     green    none     none   green
2       none      none     red     none     red