Why are solid-state relay modules different colors?

The color is used to identify the type. The open-standard color scheme was developed by Opto 22 in 1978 to help identify the four basic types available. The universally accepted colors are:

• Red: Output DC (ODC)
• White: Input DC (IDC)
• Black: Output AC (OAC)
• Yellow: Input AC (IAC)

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