Verdict: partial authority. Fuel Tax Act / Reg. 464 require labels and tags but do not prescribe a colour. The Ontario Fire Code (O. Reg. 213/07), s. 4.3.1.7(1), requires tank identification "in conformance with" the Canadian Fuels Association Colour-Symbol System — an industry document, not a CSA standard or Ontario regulation. The red-on-coloured / white-on-clear scheme is enforceable in Ontario via the Fire Code's reference to the CFA system, but the colours themselves come from an industry document, so the citation chain is Fire Code → CFA, not Fuel Tax Act.
The Ministry of Finance "issues labels and tags … to be used by any person who owns or operates any equipment used to colour, store, transport or deliver coloured fuel. Each identifying label or tag must be placed in a location where it is clearly visible under normal operating conditions." No colour is prescribed in the Act or Reg. 464.
O. Reg. 213/07 (Fire Code), Division B, s. 4.3.1.7(1) requires that storage tanks and their filling and emptying connections be identified using the Canadian Fuels Association (CFA) document "Using the Canadian Fuels Colour-Symbol System to Mark Equipment and Vehicles for Product Identification." Under that CFA system, dyed/non-taxed diesel uses a red product-identification band and clear diesel uses a white band. The red-versus-white practice is therefore enforceable in Ontario, but the authority is the CFA industry document referenced by the Fire Code.
The current edition is CSA B139 Series:24, the eleventh edition; the ANSI Standards Store preface confirms verbatim: "This is the eleventh edition of CSA B139, Installation code for oil-burning equipment. It supersedes the previous editions published in 2019, 2015, 2009, 2004, 2000, 1991, 1976, 1971, 1962, and 1957." CSA B139 is adopted in Ontario via O. Reg. 213/01 (Fuel Oil) and the TSSA Code Adoption Document. CSA B139 governs installation, venting, fill/spill, leakage inspection, and tank specifications for oil-burning equipment. It does not prescribe a red-versus-white exterior colour scheme distinguishing clear from coloured diesel.
The "red signage on coloured tanks, white signage on clear tanks" claim is supportable — but cite the Ontario Fire Code s. 4.3.1.7(1) and the CFA Colour-Symbol System, not Reg. 464 or CSA B139. Frame as a Fire Code / industry-standard requirement rather than a Fuel Tax Act requirement.
Confidence: estimated (Fire Code reference is verified; the colour assignments themselves derive from the referenced CFA industry document, not from Ontario statute directly).